CONTRIBUTING.md: add bottles, revision notes

Misc minor edits.

CONTRIBUTING.md

@@ -1,35 +1,48 @@
 # Contributing
-Thank you for your interest in contributing to [Homebrew/science]. The following guidelines are designed to help you write more efficient pull requests.
+
+Thank you for your interest in contributing to [Homebrew Science]. The following guidelines are designed to help you write more efficient pull requests.
 
 ## Formula Guidelines
-Read Homebrew's [Formula Cookbook] and [Acceptable Formulae]. If your formula installs or depends on Python modules you may want to read [Python for Formula Authors] as well.
 
-Please **follow the [GitHub Ruby Styleguide]**.
+**IMPORTANT** First read Homebrew's [Formula Cookbook] and [Acceptable Formulae]. If your formula installs or depends on Python modules read [Python for Formula Authors] as well.
+
+Homebrew follows the [GitHub Ruby Styleguide]. Check `brew style` or `brew audit --strict` before submitting a new formula.
 
 #### Patches
-Homebrew provides DSL for applying diff patches appended to the end of formula file, or as remote files (e.g. a gist). In most cases, patches should be submitted upstream and linked to in your comments.
+
+Homebrew provides DSL for applying diff patches appended to the end of formula file, or as remote files (e.g. a [Gist]). In most cases, patches should be submitted upstream and linked to in your comments.
 
 #### Tests
-All formulæ should be accompanied by tests. We greatly appreciate any submissions that improve individual tests and test coverage in Homebrew/science.
+
+All formulæ should be accompanied by tests. We greatly appreciate any submissions that improve individual tests and test coverage in Homebrew Science.
 
 The `test do` block allows for a post-build test of software functionality sandboxed within a temporary `testpath`. For example, a test program may be written and compiled, and its output checked against an expected value. Meaningful tests are preferred over simple commands like `system "foo", "-v"`.
 
-`make check` or equivalent should be enabled if the package provides it. This should become a classic:
+`make check` or equivalent should be enabled if the package provides it:
 
     option "without-check", "Disable build-time checking (not recommended)"
     ...
     system "make"
     system "make", "check" if build.with? "check"
     system "make", "install"
 
-If this target takes an inordinate amount of resources or is otherwise problematic the option can be switched to `"with-check"`, which will disable checking in the default build.
+If this target takes an inordinate amount of resources or is otherwise problematic the option can be switched to `"with-check"`, disabling `make check` in the default build.
+
+#### Revisions
+
+Adding or incrementing a [formula revision] forces a formula upgrade, for instance when breakage from an upgraded dependency necessitates rebuilding the downstream package. When upgrading a formula to a new version, however, any existing revision needs to be reset (i.e. removed).
+
+#### Bottles
+
+[Bottles] are Homebrew's pre-compiled binary packages. Please avoid making any changes to the bottle block. Bottle checksums, URLs, and revisions are handled automatically by [Brew Test Bot].
 
 ## Submitting a Pull Request
-First read core Homebrew's [How To Open a Homebrew Pull Request (and get it merged)]. The Homebrew/science tap repository is located in `$(brew --repository)/Library/Taps/homebrew/homebrew-science`.
+
+First read core Homebrew's [How To Open a Homebrew Pull Request (and get it merged)]. The Homebrew Science tap repository is located in `$(brew --repository)/Library/Taps/homebrew/homebrew-science`.
 
 Check [open pull requests] before submitting a duplicate. We prefer one formula per PR.
 
-Start you commit messages with a short informative summary, prefaced by the formula name:
+Preface your commit message with the formula name, followed by a brief summary:
 * `foo: add test`
 * `bar: make X11 optional`
 Version upgrades should just be titled with their version:
@@ -39,43 +52,51 @@ Version upgrades should just be titled with their version:
 Use the rest of the commit message to describe your changes and link to any relevant issues. When your submission is ready to merge, squash all your commits to a single commit and push to your remote branch, with `--force` if necessary.
 
 ## Pull Request vs. Tap
-Anyone can host their own [tap]. Homebrew/science may give your formula wider visibility but a tap is preferable when:
+
+Anyone can host their own tap (see [Interesting Taps & Branches]). Homebrew Science may give your formula wider visibility, but a tap is preferable when:
 * Your formula must be brewable urgently.
 * It is part of a group of specialized and/or related formulæ.
-* It is head-only or lacks a stable tagged release.
+* It is HEAD-only or lacks a stable tagged release.
 
-Feel free to start your own tap and submit to Homebrew/science later.
+Feel free to start your own tap and submit to Homebrew Science later.
 
 ## Useful Snippets and Notes
+
 #### Linking Dependencies
-Avoid refering to `HOMEBREW_PREFIX` in a formula. If you need to refer to other libraries or header files, use stable `opt` paths: `Formula["foo"].opt_prefix`, `Formula["foo"].opt_lib`,  `Formula["foo"].opt_include`, etc.
+
+Avoid refering to `HOMEBREW_PREFIX` in a formula. If you need to refer to dependency libraries or header files, use stable `opt` paths: `Formula["foo"].opt_prefix`, `Formula["foo"].opt_lib`,  `Formula["foo"].opt_include`, etc.
 
 #### OpenMP
-The current version of Clang, which is the default C compiler used in Homebrew, doesn't support OpenMP, but GCC does. Here's an example of alerting the user that OpenMP will not be enabled if using Clang:
 
-    opoo "Clang does not support OpenMP. Compile with gcc if this is not acceptable." if ENV.compiler == :clang
+The current version of clang, Homebrew's default C/C++ compiler, does not support OpenMP, but GCC does. Here's an example of alerting the user that OpenMP will not be enabled if using clang:
 
-This snippet will not abort compilation but output a warning message.
+    opoo "clang does not support OpenMP. Compile with gcc if this is not acceptable." if ENV.compiler == :clang
 
-formulæ which require OpenMP support should specify
+This snippet will not abort compilation but output a warning message.
 
-    needs :openmp
+If OpenMP support is obligatory, `needs :cxx11` may be used to avoid building with clang/LLVM altogether.
 
 #### MPI
-Depending on `:mpi` is more flexible than depending directly on `mpich2` or `open-mpi`. Remember that users could have installed either and that the two `conflict_with` each other.
+
+Depending on `:mpi` is more flexible than depending directly on `mpich2` or `open-mpi`. Remember that users could have installed either and the two `conflict_with` each other.
 
 #### Checking What Options Were Used to Build a Dependency
 
     nprocs = Tab.for_formula("foo").without?("mpi") ? 1 : 2
 
 ## Suggestions
+
 Improvements to this guide are appreciated via issues or pull requests. If you're willing to add a new section to this documentation or the wiki, we would very much welcome your contribution.
 
-[Homebrew/science]: https://github.com/Homebrew/homebrew-science
+[Homebrew Science]: https://github.com/Homebrew/homebrew-science
 [open pull requests]: https://github.com/Homebrew/homebrew-science/pulls
 [How To Open a Homebrew Pull Request (and get it merged)]: https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/How-To-Open-a-Homebrew-Pull-Request-(and-get-it-merged).md
-[tap]: https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Interesting-Taps-%26-Branches.md#interesting-taps--branches
+[Interesting Taps & Branches]: https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Interesting-Taps-%26-Branches.md#interesting-taps--branches
+[Formula revision]: https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Formula-Cookbook.md#formulae-revisions
+[Bottles]: https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Bottles.md
+[Brew Test Bot]: https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Brew-Test-Bot.md#brew-test-bot
 [GitHub Ruby Styleguide]: https://github.com/styleguide/ruby
 [Formula Cookbook]: https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Formula-Cookbook.md
 [Acceptable Formulae]: https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Acceptable-Formulae.md
-[Python for Formula Authors]: https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Python-for-Formula-Authors.md
+[Python for Formula Authors]: https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Python-for-Formula-Authors.md
+[Gist]: https://gist.github.com/