gcc/.forgejo/PULL_REQUEST_TEMPLATE.md

Thanks for taking the time to contribute to GCC!

Please be advised that https://forge.sourceware.org/ is currently a trial that is being used by the GCC community to experiment with a new workflow based on pull requests.

Pull requests sent here may be forgotten or ignored. Patches that you want to propose for inclusion in GCC should use the existing email-based workflow, see https://gcc.gnu.org/contribute.html