Fixed #34, appropriatlly document duplicate results.

docs/api.txt

@@ -62,3 +62,13 @@ like so::
 
     >>> Food.objects.filter(tags__in=["delicious"])
     [<Food: apple>, <Food: pear>, <Food: plum>]
+
+
+If you're filtering on multiple tags, it's very common to get duplicate
+results, because of the way relational databases work.  Often you'll want to
+make use of the ``distinct()`` method on ``QuerySets``::
+    
+    >>> Food.objects.filter(tags__in=["delicious", "red"])
+    [<Food: apple>, <Food: apple>]
+    >>> Food.objects.filter(tags__in=["delicious", "red"]).distinct()
+    [<Food: apple>]