Update CONTRIBUTING.md

CONTRIBUTING.md

-# CONTRIBUTING TO THE IRIS COQ DEVELOPMENT
+# Contributing to the Iris Coq Development
 
 Discussion about the Iris Coq development happens on the mailing list
 [iris-club@lists.mpi-sws.org](https://lists.mpi-sws.org/listinfo/iris-club) and
@@ -8,9 +8,9 @@ place to ask questions.  The chat requires an account at the
 tab).
 
 If you want to report a bug, please use the
-[issue tracker](https://gitlab.mpi-sws.org/FP/iris-coq/issues).  To contribute
-code, please send your MPI-SWS GitLab username to
-[Ralf Jung](https://gitlab.mpi-sws.org/jung) to enable personal projects for
-your account.  Then you can fork the
+[issue tracker](https://gitlab.mpi-sws.org/FP/iris-coq/issues), which also
+requires a GitLab account.  To contribute code, please send your MPI-SWS GitLab
+username to [Ralf Jung](https://gitlab.mpi-sws.org/jung) to enable personal
+projects for your account.  Then you can fork the
 [Iris git repository](https://gitlab.mpi-sws.org/FP/iris-coq/), make your
 changes in your fork, and create a merge request.