[llvm] [docs] Add beginner-focused office hours (PR #80308)

[Kristof Beyls via llvm-commits]

kbeyls wrote:

I think this is great, thank you for organizing this!

One potential tweak that might be helpful, I'm not fully sure, would be to explicitly name the people who are the rotating hosts. My thinking there is that it might slightly lower the anxiety level for some newcomers when dialing in to these office hours, when they have an idea of who the host might be.

https://github.com/llvm/llvm-project/pull/80308