Create an openmp-wg GitHub repo

As discussed in https://discourse.llvm.org/t/where-should-wg-meeting-materials-live/88913, I'd like to request that `openmp-wg` repo be created in the LLVM organization. The purpose of it is to host meeting minutes and other materials relevant to the development of OpenMP support in LLVM.

The initial maintainers will be Krzysztof Parzyszek (@kparzysz), Michael Klemm (@mjklemm), and Kiran Kumar T P (@kiranktp).

Read the linked Discourse discussion to understand the agreed location for OpenMP working-group materials. Verify the requested openmp-wg repository name and the three initial maintainers, then confirm that the repository is created in the LLVM organization and is ready to host meeting minutes and related materials.

Written by the indexing model from the issue text.