[clang] [docs] Convert Maintainers.rst to Markdown (.md) (PR #180652)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I don't really have an opinion here?  I hate ALL markup languages equally.

But as far as a document, it seems fine to me?  This is probably an Aaron decision, though I cannot believe he'd care that much. 


https://github.com/llvm/llvm-project/pull/180652