Add link to gitlab in community

Since it's the most active place for Apertis development

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

content/policies/community.md

@@ -24,6 +24,8 @@ The best ways to get in touch with the community are through:
         is the place to discuss Apertis development and project.
       - If you are interested in adding a new mailing list, please
         contact *listmaster at apertis.org*.
+  - [Apertis GitLab](https://gitlab.apertis.org/)
+      - It is where development and most technical discussions take place.
 
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