phase: use standard syntax for command line flags

We don't mark them as literal text and we mention the short option the
first time we talk about a given flag.

mercurial/commands.py

@@ -4228,7 +4228,7 b' def phase(ui, repo, *revs, **opts):'
 
     With no argument, show the phase name of specified revisions.
 
-    With one of ``--public``, ``--draft`` or ``--secret``, change the
+    With one of -p/--public, -d/--draft or -s/--secret, change the
     phase value of the specified revisions.
 
     Unless -f/--force is specified, :hg:`phase` won't move changeset from a