[llvm] [docs] Refresh Developer Policy text (PR #136198)

[Aaron Ballman via llvm-commits]

AaronBallman wrote:

> which is the closest thing we have on how to run an RFC.

FYI:
https://clang.llvm.org/get_involved.html#criteria, starting from `The Clang community uses an RFC process `

https://github.com/llvm/llvm-project/pull/136198