Docs: Incoming e-mails: require gitlab-ctl restart

See https://gitlab.com/gitlab-org/gitlab-ce/issues/23560#note_61966788

doc/administration/incoming_email.md

@@ -187,6 +187,7 @@ for a real-world example of this exploit.
 
     ```sh
     sudo gitlab-ctl reconfigure
+    sudo gitlab-ctl restart
     ```
 
 1. Verify that everything is configured correctly: