Merge topic 'github-pr-template'

7983e068 Add GitHub PR template to point contributors at CONTRIBUTING.rst

Acked-by: Kitware Robot <kwrobot@kitware.com>
Reviewed-by: Ben Boeckel <ben.boeckel@kitware.com>
Reviewed-by: Craig Scott <craig.scott@crascit.com>
Merge-request: !1125

.github/pull_request_template.md

+Thanks for your interest in contributing to CMake!  The GitHub repository
+is a mirror provided for convenience, but CMake does not use GitHub pull
+requests for contribution.  Please see
+
+  https://gitlab.kitware.com/cmake/cmake/tree/master/CONTRIBUTING.rst
+
+for contribution instructions.  GitHub OAuth may be used to sign in.