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

[Mehdi Amini via llvm-commits]

================
@@ -46,11 +73,106 @@ The default commit message for a squashed pull request is the pull request
 description, so this will allow reviewers to review the commit message before
 approving the commit.
 
+When pushing to your branch, make sure you push to the correct fork. Check your
+remotes with:
+
+::
+
+  git remote -v
+
+And make sure you push to the remote that's pointing to your fork.
+
+Rebasing Pull Requests and Force Pushes
+---------------------------------------
+In general, you should avoid rebasing a Pull Request and force pushing to the
+branch that's the root of the Pull Request during the review. This action will
+make the context of the old changes and comments harder to find and read.
----------------
joker-eph wrote:

I don't think this is a good advice here, unless you explicitly say: "you  should merge `origin/main` into your branch regularly".

Otherwise you may run into conflicts, or mid-air collision: any `ninja check` you run locally isn't testing against the latest `main` either.
It's not even clear what the pre-merge CI would test: would it be an outdated version of the code?

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