Update CONTRIBUTING.md (#31590)

Summary:
Add more detail about requesting review in the contribution guide.
In the GAAD initiative it's particularly useful to know when certain PRs need our attention so wanted to highlight the code review process to remind contributors to request reviewers.

## Changelog

[General] [Added] - Added more detail about the review process

Pull Request resolved: #31590

Test Plan: Grammar, clarity review

Reviewed By: TheSavior

Differential Revision: D28719869

Pulled By: lunaleaps

fbshipit-source-id: 9213fefbe602588f9e5cee7ba240b93bc7f291b5

Author: Luna Wei

CONTRIBUTING.md

@@ -86,6 +86,7 @@ The process of proposing a change to React Native can be summarized as follows:
 8. Create a pull request to the React Native repository.
 9. Review and address comments on your pull request.
     1. A bot may comment with suggestions. Generally we ask you to resolve these first before a maintainer will review your code.
+    2. If changes are requested and addressed, please [request review](https://docs.github.com/en/github/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/requesting-a-pull-request-review) to notify reviewers to take another look.
 10. If you haven't already, please complete the [Contributor License Agreement](https://github.com/facebook/react-native/wiki/Contributor-License-Agreement) ("CLA"). **[Complete your CLA here.](https://code.facebook.com/cla)**
 
 If all goes well, your pull request will be merged. If it is not merged, maintainers will do their best to explain the reason why.