[llvm] [Doc] Add a section on CI to the GitHub documentation (PR #85376)

[Nikita Popov via llvm-commits]

================
@@ -124,12 +124,24 @@ For developers to commit changes from Git
 -----------------------------------------
 
 Once a patch is reviewed, you can select the "Squash and merge" button in the
-GitHub web interface. You might need to rebase your change before pushing
-it to the repo.
+GitHub web interface.
 
-LLVM currently has a linear-history policy, which means that merge commits are
-not allowed. The `llvm-project` repo on github is configured to reject pushes
-that include merges, so the `git rebase` step above is required.
+When pushing directly from the command-line to the `main`` branch, you will need
----------------
nikic wrote:

```suggestion
When pushing directly from the command-line to the ``main`` branch, you will need
```

https://github.com/llvm/llvm-project/pull/85376