Add link to issue queue

tasks/main.yml

 # Add Mattermost:
+# - https://gitlab.com/gitlab-org/gitlab-mattermost/issues
 # - http://doc.gitlab.com/omnibus/gitlab-mattermost/
 # - http://www.mattermost.org/community-applications/
 # - https://github.com/NotSqrt/mattermost-integration-gitlab
@@ -7,7 +8,6 @@
 #   - https://forum.mattermost.org/t/help-wanted-test-new-apache-instructions/878
 # Enable module proxy_wstunnel
 
-
 ---
 - name: install prerequisites
   become: yes