doc: clarify the review and landing process

Adds/mentions:
- Link to glossary
- Commit squashing and CI run
- 48/72 hour wait and PR review feature
- Extra notes section
- "Landed in <sha>" comment

PR-URL: #10202
Ref: #10151
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

Author: joyeecheung

CONTRIBUTING.md

@@ -248,18 +248,85 @@ If in doubt, you can always ask for guidance in the Pull Request or on
 [IRC in the #node-dev channel](https://webchat.freenode.net?channels=node-dev&uio=d4).
 
 Feel free to post a comment in the Pull Request to ping reviewers if you are
-awaiting an answer on something.
+awaiting an answer on something. If you encounter words or acronyms that
+seem unfamiliar, check out this
+[glossary](https://sites.google.com/a/chromium.org/dev/glossary).
 
+Note that multiple commits often get squashed when they are landed (see the
+notes about [commit squashing](#commit-squashing)).
 
 ### Step 8: Landing
 
-Once your Pull Request has been reviewed and approved by at least one Node.js
-Collaborators (often by saying LGTM, or Looks Good To Me), and as long as
-there is consensus (no objections from a Collaborator), a
-Collaborator can merge the Pull Request . GitHub often shows the Pull Request as
- `Closed` at this point, but don't worry. If you look at the branch you raised
- your Pull Request against (probably `master`), you should see a commit with
- your name on it. Congratulations and thanks for your contribution!
+In order to get landed, a Pull Request needs to be reviewed and
+[approved](#getting-approvals-for-your-pull-request) by
+at least one Node.js Collaborator and pass a
+[CI (Continuous Integration) test run](#ci-testing).
+After that, as long as there are no objections
+from a Collaborator, the Pull Request can be merged. If you find your
+Pull Request waiting longer than you expect, see the
+[notes about the waiting time](#waiting-until-the-pull-request-gets-landed).
+
+When a collaborator lands your Pull Request, they will post
+a comment to the Pull Request page mentioning the commit(s) it
+landed as. GitHub often shows the Pull Request as `Closed` at this
+point, but don't worry. If you look at the branch you raised your
+Pull Request against (probably `master`), you should see a commit with
+your name on it. Congratulations and thanks for your contribution!
+
+## Additional Notes
+
+### Commit Squashing
+
+When the commits in your Pull Request get landed, they will be squashed
+into one commit per logical change, with metadata added to the commit
+message (including links to the Pull Request, links to relevant issues,
+and the names of the reviewers). The commit history of your Pull Request,
+however, will stay intact on the Pull Request page.
+
+For the size of "one logical change",
+[0b5191f](https://github.com/nodejs/node/commit/0b5191f15d0f311c804d542b67e2e922d98834f8)
+can be a good example. It touches the implementation, the documentation,
+and the tests, but is still one logical change. In general, the tests should
+always pass when each individual commit lands on the master branch.
+
+### Getting Approvals for Your Pull Request
+
+A Pull Request is approved either by saying LGTM, which stands for
+"Looks Good To Me", or by using GitHub's Approve button.
+GitHub's Pull Request review feature can be used during the process.
+For more information, check out
+[the video tutorial](https://www.youtube.com/watch?v=HW0RPaJqm4g)
+or [the official documentation](https://help.github.com/articles/reviewing-changes-in-pull-requests/).
+
+After you push new changes to your branch, you need to get
+approval for these new changes again, even if GitHub shows "Approved"
+because the reviewers have hit the buttons before.
+
+### CI Testing
+
+Every Pull Request needs to be tested
+to make sure that it works on the platforms that Node.js
+supports. This is done by running the code through the CI system.
+
+Only a Collaborator can request a CI run. Usually one of them will do it
+for you as approvals for the Pull Request come in.
+If not, you can ask a Collaborator to request a CI run.
+
+### Waiting Until the Pull Request Gets Landed
+
+A Pull Request needs to stay open for at least 48 hours (72 hours on a
+weekend) from when it is submitted, even after it gets approved and
+passes the CI. This is to make sure that everyone has a chance to
+weigh in. If the changes are trivial, collaborators may decide it
+doesn't need to wait. A Pull Request may well take longer to be
+merged in. All these precautions are important because Node.js is
+widely used, so don't be discouraged!
+
+### Check Out the Collaborator's Guide
+
+If you want to know more about the code review and the landing process,
+you can take a look at the
+[collaborator's guide](https://github.com/nodejs/node/blob/master/COLLABORATOR_GUIDE.md).
 
 <a id="developers-certificate-of-origin"></a>
 ## Developer's Certificate of Origin 1.1