Add note about updating GDK settings

config/gitlab.yml.example

@@ -9,6 +9,8 @@
 # If you change this file in a merge request, please also create       #
 # a MR on https://gitlab.com/gitlab-org/omnibus-gitlab/merge_requests. #
 # For more details see https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/doc/settings/gitlab.yml.md #
+# Be sure to create a MR against the GDK configuration                 #
+# file (support/templates/gitlab/config/gitlab.yml.erb) too.           #
 ########################################################################
 #
 #