Add shortcut to merge requests

wiki/src/shortcuts.mdwn

@@ -90,6 +90,7 @@ ikiwiki will include your shortcut in the standard underlay.
   url="https://gitlab.tails.boum.org/groups/tails/-/issues?scope=all&utf8=✓&state=opened&label_name[]=Starter"
   desc="list of *Starter* tasks"]]
 * [[!shortcut name=tails_ticket url="https://gitlab.tails.boum.org/tails/tails/-/issues/%S" desc="#%s"]]
+* [[!shortcut name=tails_mr url="https://gitlab.tails.boum.org/tails/tails/-/merge_requests/%S" desc="!%s"]]
 * [[!shortcut name=tails_roadmap url="https://tails.boum.org/contribute/roadmap" desc="roadmap"]]
 * [[!shortcut name=tails_gitweb url="https://gitlab.tails.boum.org/tails/tails/-/blob/master/%S"]]
 * [[!shortcut name=tails_gitweb_dir url="https://gitlab.tails.boum.org/tails/tails/-/tree/master/%S"]]