This way, we don't need to remove the contents of the ReleaseNotes file
after the branch. This should make it much easier and natural to cherry-pick
changes onto the release branch. Typically, we need two patches for those.
First, we need the code changes against `main`, and then we need a patch
that updates the release notes on the just-created branch.
By versioning the release notes, it becomes easy to author a change
against `main` that targets a just-branched LLVM release by simply
adding it to the release notes for the right version. This has been
a pain point in previous releases.
Differential Revision: https://reviews.llvm.org/D155024
