[llvm] [Docs] Update Maintainer in Developer Policy (PR #154687)

[Renato Golin via llvm-commits]

rengolin wrote:

> Thanks for working on this, but we'll need this to go through the usual RFC process too. Can you post an RFC to Discourse and then link that post with this PR?

We already have one:
https://discourse.llvm.org/t/maintainer-policy-discussion/87663

https://github.com/llvm/llvm-project/pull/154687