patchbomb: mark ancient option deprecated

This just exists for backwards compatibility with the earliest
versions of patchbomb.

hgext/patchbomb.py

@@ -514,6 +514,7 b' def patchbomb(ui, repo, *revs, **opts):'
     def genmsgid(id):
         return '<%s.%s@%s>' % (id[:20], int(start_time[0]), socket.getfqdn())
 
+    # deprecated config: patchbomb.from
     sender = (opts.get('from') or ui.config('email', 'from') or
               ui.config('patchbomb', 'from') or
               prompt(ui, 'From', ui.username()))