strip: update help to state than you can strip public changeset

Multiple people have been confused by it.

hgext/mq.py

@@ -2844,6 +2844,10 b' def strip(ui, repo, *revs, **opts):'
     Use the --no-backup option to discard the backup bundle once the
     operation completes.
 
+    Strip is not a history-rewriting operation and can be used on
+    changesets in the public phase. But if the stripped changesets have
+    been pushed to a remote repository you will likely pull them again.
+
     Return 0 on success.
     """
     backup = 'all'