docs: remove mailing list as way of submitting patches

All developers now use gitlab, don't confuse newcomers by suggesting
they might use the mailing list. We want everyone to use gitlab so
that patches get run through basic CI before they are merged.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Dylan Baker <dylan@pnwbakers.com>
diff --git a/README.rst b/README.rst
index 4ccd72e..9e44d78 100644
--- a/README.rst
+++ b/README.rst
@@ -56,5 +56,4 @@
 documentation (`docs/submittingpatches.html
 <https://mesa3d.org/submittingpatches.html>`_).
 
-Note that Mesa uses email mailing-lists for patches submission, review and
-discussions.
+Note that Mesa uses gitlab for patches submission, review and discussions.