[llvm] [llvm][docs] Document how to ask for things other than commit access (PR #146340)

[Aaron Ballman via llvm-commits]

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

Thank you for improving the docs, in general I like the direction this is going! Please wait a bit before landing in case others have comments they'd like to raise.

https://github.com/llvm/llvm-project/pull/146340