[PATCH 3 of 6] perftest: document the perfrevset command

[pierre-yves.david at logilab.fr]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at logilab.fr>
# Date 1357323735 -3600
# Node ID a5761473ca07eb18e304e804d40804c7799c7a5c
# Parent  805c71aa0bd6c4fe19f2314454f068a6d79e4c8f
perftest: document the perfrevset command

I'll add an argument to it.

diff --git a/contrib/perf.py b/contrib/perf.py
--- a/contrib/perf.py
+++ b/contrib/perf.py
@@ -259,10 +259,12 @@ def perfrevlog(ui, repo, file_, **opts):
         for x in xrange(0, len(r), dist):
             r.revision(r.node(x))
 
     timer(d)
 
- at command('perfrevset')
+ at command('perfrevset',[],
+         "REVSET")
 def perfrevset(ui, repo, expr):
+    """benchmark the execution time of a revset"""
     def d():
         repo.revs(expr)
     timer(d)