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

[Tom Stellard via llvm-commits]

================
@@ -21,21 +24,45 @@ 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 compelete
+documentation refer to `GitHubs 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>`_
 of the llvm-project and
 `create a pull request from the fork <https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request-from-a-fork>`_.
 
+Creating Pull Requests with GitHub CLI
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+With the CLI it's enough to create the branch locally and then run:
----------------
tstellar wrote:

We currently only allow squash and merge for pull requests, I think this is a good policy because it makes it harder to make a mistake and accidentally push a series of fixup commits.  Even with this setting though, it's still possible to have a pull request with multiple commits from the start, you just have to push it manually once it's reviewed rather than going through the PR interface.

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