[Office Hours] add initial guidance for hosts

[kristof.beyls]

Summary

This includes adding guidance to announce an office hours session on the
Discord channel, as discussed at the office hours round table at EuroLLVM 2022,
see https://discourse.llvm.org/t/office-hours-eurollvm-round-table-summary/62480.

Fixes #55423

[kristof.beyls]

Use correct syntax to indicate we're adding a subsubsection, not a section, see https://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html#sections

[aaron.ballman]

llvm/docs/GettingInvolved.rst

293–294

We should also request people mention it on the IRC channel as that's the other official communication place. However, it brings up an interesting question of how to handle the fact that there are people who only use one of the two services.

297–300

[kristof.beyls]

llvm/docs/GettingInvolved.rst

293–294

Fair point. I'll look into rephrasing this such that it's clear this is just "guidance" and not required. If the host happens to be on one or both of Discord and/or IRC, it's a useful, low-cost thing to do to announce the office hour starting there.

[kristof.beyls]

updated guidance based on Aaron's feedback.

[aaron.ballman]

LGTM, thank you!

[edward-jones]

llvm/docs/GettingInvolved.rst

289

Just a minor thought, but is it worth also prodding hosts to keep in mind that they should remove themselves from this list if they become unavailable? I realise if someone becomes inactive in their stated office hours they're probably not going to remember to update this, but maybe it could prompt someone if they realize they've not been able to make a few of their slots.

Regardless, I think the wording here is good.

[kristof.beyls]

llvm/docs/GettingInvolved.rst

289

Good suggestion, thank you. I've added a bullet point and committed it.

[kristof.beyls]

committed as https://github.com/llvm/llvm-project/commit/ac2f0a6f1d4b3f5ff61dac33d9aba395d79b6a3d

llvm/docs/GettingInvolved.rst

* - Tobias Grosser
     - `Video Call <https://meet.grosser.science/LLVMOfficeHours>`__
     - English, German, Spanish, French
   * - Anastasia Stulova
     - Clang internals for C/C++ language extensions and dialects, OpenCL, GPU, SPIR-V, how to contribute, women in compilers. 
     - Monthly, 2nd Thursday of the month at 17:00 BST - London time (9:00am PT except for 2 weeks in spring), 1 hour slot.
     - `GoogleMeet <https://meet.google.com/kdy-fdbv-nuk>`__
     - English, Russian, German (not fluently)
 
+
+Guidance for office hours hosts
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* If you're interested in becoming an office hours host, please add your
+  information to the list above.
+* When starting an office hours session, please type something like "*Hi,
+  I'm available for chats in the next half hour at* video chat URL. *I'm
+  looking forward to having conversations on the video chat or here.*" on the
+  `#office-hours Discord channel
+  <https://discord.com/channels/636084430946959380/976196303681896538>`__.
+
+  Doing this can help:
+    * overcome potential anxiety to call in for a first time.
+    * people who prefer to first exchange a few messages through text chat
+      before dialling in.
+    * remind the wider community that office hours do exist.
+
+
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