GitLab: add "Add SSH key" step to "Getting started"

wiki/src/contribute/working_together/GitLab.mdwn

@@ -20,8 +20,11 @@ desc="registration page"]] in a web browser.
 Then you will be allowed to open new issues, create merge requests, and fork
 your own copy of our repositories.
 
-Later on, you will probably need to [[request more
-credentials|GitLab#request-access]].
+Later on, you will probably need to:
+
+ - [[!tails_gitlab profile/keys desc="Add your SSH key"]]
+   to your GitLab account
+ - [[Request more credentials|GitLab#request-access]]
 
 The first time you connect over SSH to a Git repository hosted on our GitLab,
 you will be prompted to verify the server's SSH host key. Here are the