Update usage.rst

Make the advantages of django-simple-history over django-reversion clear (this was the reason why I choose django-simple-history).

Author: gabn88

docs/usage.rst

@@ -168,3 +168,5 @@ records for all ``Choice`` instances can be queried by using the manager on the
     <simple_history.manager.HistoryManager object at 0x1cc4290>
     >>> Choice.history.all()
     [<HistoricalChoice: Choice object as of 2010-10-25 18:05:12.183340>, <HistoricalChoice: Choice object as of 2010-10-25 18:04:59.047351>]
+    
+Because the history is model, you can also filter it like regulary QuerySets, a.k. Choice.history.filter(choice_text='Not Much') will work!