[llvm] [Docs] Update documentation for the new GitHub workflow (PR #65162)

[Nick Desaulniers via llvm-commits]

================
@@ -21,36 +24,194 @@ branches being used for "stacked" pull requests will be allowed.
 
 Pull Requests
 =============
-The LLVM Project does not currently accept pull requests for the llvm/llvm-project
-repository.  However, there is a
-`plan <https://discourse.llvm.org/t/code-review-process-update/63964>`_ to move
-to pull requests in the future.  This section documents the pull request
-policies LLVM will be adopting once the project starts using them.
+The LLVM project is using GitHub Pull Requests for Code Reviews. This document
+describes the typical workflow of creating a Pull Request and getting it reviewed
+and accepted. This is meant as an overview of the GitHub workflow, for complete
+documentation refer to `GitHub's documentation <https://docs.github.com/pull-requests>`_.
+
+GitHub Tools
+------------
+You can interact with GitHub in several ways: via git command line tools,
+the web browser, `GitHub Desktop <https://desktop.github.com/>`_, or the
+`GitHub CLI <https://cli.github.com>`_. This guide will cover the git command line
+tools and the GitHub CLI. The GitHub CLI (`gh`) will be most like the `arc` workflow and
+recommended.
 
 Creating Pull Requests
-^^^^^^^^^^^^^^^^^^^^^^
-For pull requests, please push a branch to your
-`fork <https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks>`_
+----------------------
+Keep in mind that each pull request should generally only contain one commit.
----------------
nickdesaulniers wrote:

This seems to contradict advice later in the page about updating commits to contains multiple commits rather than rebasing.

Maybe this can be reworded slightly to clarify that the introduction of a new pull request should only contain one commit, but that more commits may be added to address code review feedback?

https://github.com/llvm/llvm-project/pull/65162