docs: suggest installing corepack and using yarn for installing deps (#1001)

Author: trivikr

CONTRIBUTING.md

@@ -30,11 +30,12 @@ To send us a pull request, please:
 
 1. Fork the repository.
 2. Use [ASTExplorer](https://astexplorer.net/) with category `JavaScript` and parser `acorn` for examining the AST.
-3. Modify the source; please focus on the specific change you are contributing.
-4. Ensure local tests pass.
-5. Commit to your fork using clear commit messages.
-6. Send us a pull request, answering any default questions in the pull request interface.
-7. Pay attention to any automated CI failures reported in the pull request, and stay involved in the conversation.
+3. Globally install `npm i -g corepack`, and run `yarn` for installing dependencies.
+4. Modify the source; please focus on the specific change you are contributing.
+5. Ensure local tests pass.
+6. Commit to your fork using clear commit messages.
+7. Send us a pull request, answering any default questions in the pull request interface.
+8. Pay attention to any automated CI failures reported in the pull request, and stay involved in the conversation.
 
 GitHub provides additional document on [forking a repository](https://help.github.com/articles/fork-a-repo/) and
 [creating a pull request](https://help.github.com/articles/creating-a-pull-request/).