DOCS-4138: clarifying step permissions

Author: Sam Kleinman

source/includes/steps-perform-maintenance-task-on-replica-set-members.yaml

@@ -17,6 +17,9 @@ pre: |
 action:
   language: sh
   code: mongod --port 37017 --dbpath /srv/mongodb
+post: |
+  Always start :program:`mongod` with the same user, even when
+  restarting a replica set member as a standalone instance.
 ---
 title: Perform maintenance operations on the secondary.
 stepnum: 3