[clang-tools-extra] [llvm] [clang-tools-extra][docs] Convert maintainers file to Markdown (PR #200365)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

The RFC has not yet been accepted and has opposition, and this PR was accepted by the RFC author, so this was premature to land (also, it would have been nice to give me more than just the weekend to respond to the PR as lead for clang-tools-extra...). I don't think we need to revert, but please wait for the RFC to be accepted before landing more changes in response to the RFC.

https://github.com/llvm/llvm-project/pull/200365