[llvm] [llvm][docs] Convert LLVM release notes to Markdown (PR #109107)

[David Spickett via llvm-commits]

DavidSpickett wrote:

If you are here wondering why you now have a merge conflict, to convert your release note to Markdown you probably just need to replace the link and plain text syntax:
https://www.markdownguide.org/basic-syntax/#links
https://www.markdownguide.org/basic-syntax/#code

This can be previewed on GitHub to check you have done this correctly ("view file" in the code review section I think).

https://github.com/llvm/llvm-project/pull/109107