[llvm] Update GitHub PR Greeter (PR #194307)

[Andrzej Warzyński via llvm-commits]

banach-space wrote:

> > Remove the note about adding reviewers, since most projects now use code owners and reviewers are added automatically.
> 
> I don't think this is really true outside of MLIR and BOLT. Very little of LLVM uses code owners.
> 
> Overall, this seems like the right direction though.

That's a good point - sorry for missing that and thanks for pointing it out! 

It sounds like we should restore that information, which takes me further away from my goal of keeping this concise. That's unfortunate, but for a good reason. See this [commit](https://github.com/llvm/llvm-project/pull/194307/changes/ad29f6d3c026505bbb894b837b1822f32be42726) that adds an FAQ section - that's basically my attempt to structure the extra info (I pretty much restored everything).

WDYT?

https://github.com/llvm/llvm-project/pull/194307