Advertize the existence of office hours further

[kbeyls]

Places the existence of office hours could be advertized:
i. The llvm.org home page website
ii. The llvm.org "Getting started" page
iii. Maybe this could be mentioned in some of the future community.o meetings, when it fits the topic?
iv. On the LLVM github page.
v. Maybe a pinned text in an appropriate place on Discord is possible?
vi. Maybe mention the existence of office hours in LLVM Weekly.

[llvmbot]

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