[llvm] [QualGroup][docs] Document decision-taking process and refresh sync-up materials (PR #163122)

[Carlos Andres Ramirez via llvm-commits]

https://github.com/CarlosAndresRamirez commented:

Please consider the changes suggested by Wendi. That aside, it looks good to me.

https://github.com/llvm/llvm-project/pull/163122