[llvm] [docs] Add documentation for LLVM Qualification Group (PR #145331)

[Kristof Beyls via llvm-commits]

https://github.com/kbeyls approved this pull request.

Overall, this looks good to me.
I added a few suggestions inline, but most of them can be addressed in separate, later commits/improvements.
If it helps to get the group up and running by committing this as is, please do so.

https://github.com/llvm/llvm-project/pull/145331