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

[Natalie Chouinard via llvm-commits]

sudonatalie wrote:

I've also just added it to the LLVM Community Calendar (starting Feb 13): https://calendar.google.com/calendar/u/0/embed?src=calendar@llvm.org

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