add patch by Alex

content/join-us.md

@@ -21,6 +21,9 @@ For other operating systems, the [same page](/build-it/) page provides extra lin
 ### Contributing code
 
 For contributions, the best way to hand them in is via our GitLab instance [invent.kde.org](https://invent.kde.org/utilities/kate).
+
+How to set it up and use it is documented in the [invent.kde.org documentation](https://community.kde.org/Infrastructure/GitLab).
+
 Just open a new [merge request](https://invent.kde.org/utilities/kate/merge_requests) there for Kate.
 For more details about this, refer to [this blog post](/post/2020/2020-07-18-contributing-via-gitlab-merge-requests/).