[llvm] [Docs] Add CIR related meetings to GettingInvolved page (PR #157181)

[Bruno Cardoso Lopes via llvm-commits]

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@@ -213,6 +213,15 @@ what to add to your calendar invite.
      - `ics <https://calendar.google.com/calendar/ical/c_fe5774fa2769c5085d6b87e8fac272e8940e7d0089bc0e0a58dc3ead7978504b%40group.calendar.google.com/public/basic.ics>`__
        `gcal <https://calendar.google.com/calendar/embed?src=c_fe5774fa2769c5085d6b87e8fac272e8940e7d0089bc0e0a58dc3ead7978504b%40group.calendar.google.com&ctz=Asia%2FTokyo>`__
      - `Minutes/docs <https://discourse.llvm.org/t/llvm-qualification-wg-sync-ups-meeting-minutes/87148>`__
+   * - MLIR C/C++ Frontend Working Group
+     - 1st Monday of the month (usually)
+     - `ics <https://calendar.google.com/calendar/ical/jvceakm3kbpku3f4jrsv1lkigo%40group.calendar.google.com/public/basic.ics>`__
+       `gcal <https://calendar.google.com/calendar/embed?src=jvceakm3kbpku3f4jrsv1lkigo%40group.calendar.google.com&ctz=America%2FLos_Angeles>`__
+     - `Minutes/docs <https://docs.google.com/document/d/1-flHK3TjQUrkSO2Fdt4webZ2zCyeXxpTLMiRQbMW7hE>`__
+   * - ClangIR Upstreaming Coordination Meeting
+     - Every 2 weeks on Mondays
+     -
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bcardosolopes wrote:

This worked for me:
> Open a web browser and go to [Google Calendar](https://calendar.google.com/). Click the Settings icon (gear) in the top right, then select Settings. In the left-hand panel, under "Settings for my calendars," click the name of the calendar you wish to share. Under the "Access permissions for events" section, ensure the box for "Make available to public" is checked.  Scroll down to the "Integrate calendar" section and find the "Public address in iCal format" URL. Copy this link.

https://github.com/llvm/llvm-project/pull/157181