[GettingInvolved] Add wg-hlsl to online sync ups (#205891)

This has been on the community calendar for a very long time, but
apparently we never added it here.

llvm/docs/GettingInvolved.md

@@ -256,6 +256,10 @@ what to add to your calendar invite.
      - [ics](https://calendar.google.com/calendar/ical/2d77f9a2624d18cd46e5299d15cc0fa0c90dca53fd68802261d52121d21a0573%40group.calendar.google.com/public/basic.ics)
        [gcal](https://calendar.google.com/calendar/u/0?cid=MmQ3N2Y5YTI2MjRkMThjZDQ2ZTUyOTlkMTVjYzBmYTBjOTBkY2E1M2ZkNjg4MDIyNjFkNTIxMjFkMjFhMDU3M0Bncm91cC5jYWxlbmRhci5nb29nbGUuY29t)
      - [Meeting notes](https://docs.google.com/document/d/1DkCik6BTnO-cox_9y_BTKzPaJJOo_hBxiNFP3lInvOM/edit?tab=t.nvvd6cfloi81)
+   * - [HLSL Working Group](https://github.com/llvm/wg-hlsl)
+     - Every week on Thursday
+     -
+     - [Meeting notes](https://github.com/llvm/wg-hlsl/tree/main/meetings)
 ```
 
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