update CONTRIBUTING

CONTRIBUTING.md

@@ -6,8 +6,9 @@ You will have to create an account at the
 [MPI-SWS GitLab](https://gitlab.mpi-sws.org/users/sign_in) (use the "Register"
 tab).
 
-To contribute code, please contact [Ralf Jung](https://gitlab.mpi-sws.org/jung)
-to enable personal projects for your account.  Then you can fork the
+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
 [Coq-std++ git repository](https://gitlab.mpi-sws.org/robbertkrebbers/coq-stdpp),
 make your changes in your fork, and create a merge request.