This meeting never quite took off the way I had hoped, and I haven't had
time for it in quite a while, so I am removing it from the Getting
Involved page.

By far the most important part of this patch is updating
GettingInvolved.rst to include the invite link, but I've grepped for any
other discord.com links.

I'm no Discord expert, but from my experience (confirmed via @preames
kindly testing as well) the direct channel links provide a confusing
experience if you haven't already found and used an invite link to the
LLVM Discord server. If you're logged into Discord but not a member of
LLVM's sever, the web app opens and then...nothing. No channel opens, no
prompt to join the server or even a hint that you need to find an invite
link (and if you're not used to Discord, you likely don't even know
that's necessary).

This patch addresses the issue by providing the invite link where
Discord is mentioned.

The LLVM Discord bot now has the ability to scrape the LLVM calendar &
send reminders about upcoming office hours events and sync-ups. Document
that here.

While I'm in the area, add a note about the bot's ability to @mention
people when they're on buildbot blamelists.

Related to llvm/Community.o#19

Unfortunately, due to other commitments I am no longer able to host this
community meeting.

Co-authored-by: Anastasia Stulova <astulova@nvidia.com>

This does not touch code owners or credits files that list IRC handles,
that can be done separately if we want to make that change.

See
https://discourse.llvm.org/t/rfc-remove-irc-as-a-recommended-communication-channel/82808/3
for the RFC.

The WebEx link will become invalid soon, we are switching to Google
Meet. Also, changing the cadence from biweekly to monthly.