Clarify permission for trains on protected branch

doc/ci/pipelines/merge_trains.md

@@ -35,7 +35,8 @@ If the pipeline for the merge request at the front of the train completes succes
 the changes are merged into the target branch, and the other pipelines continue to
 run.
 
-To add a merge request to a merge train, you need [permissions](../../user/permissions.md) to push to the target branch.
+To add a merge request to a merge train, you need [permissions](../../user/permissions.md) to merge or push to the 
+target branch.
 
 Each merge train can run a maximum of **twenty** pipelines in parallel.
 If more than twenty merge requests are added to the merge train, the merge requests