docs: update dev instructions for the repo (angular#13890)

DEV_ENVIRONMENT.md

@@ -1,9 +1,10 @@
 # Developer guide: getting your environment set up
 
-1. Make sure you have `node` installed with a version at _least_ 5.5.0.
+1. Make sure you have `node` installed with a version at _least_ 10.0.0 and `yarn` with a version
+   of at least 1.10.0. We recommend using `nvm` to manage your node versions.
 2. Run `yarn global add gulp` to install gulp.
-3. Fork the `angular/material2` repo.
-4. Clone your fork.
+3. Fork the `angular/material2` repo on GitHub.
+4. Clone your fork to your machine with `git clone`.
    Recommendation: name your git remotes `upstream` for `angular/material2`
    and `<your-username>` for your fork. Also see the [team git shortcuts](https://github.com/angular/material2/wiki/Team-git----bash-shortcuts).
 5. From the root of the project, run `yarn`.
@@ -20,7 +21,3 @@ and rebuild. The browser should refresh automatically when changes are made.
 To run unit tests, run `gulp test`.
 To run the e2e tests, run `gulp e2e`.
 To run lint, run `gulp lint`.
-
-
-### Running benchmarks
-Not yet implemented.