Merge pull request mbleigh#175 from rromanchuk/patch-1

Clarify ownership with a few more examples. RE: object.tags returning [] due to NULL in join

README.rdoc

@@ -149,8 +149,10 @@ Tags can have owners:
     @some_user.tag(@some_photo, :with => "paris, normandy", :on => :locations)
     @some_user.owned_taggings
     @some_user.owned_tags
-    @some_photo.locations_from(@some_user)
-
+    @some_photo.locations_from(@some_user) # => ["paris", "normandy"]
+    @some_photo.owner_tags_on(@some_user, :locations) # => [#<ActsAsTaggableOn::Tag id: 1, name: "paris">...]
+    @some_photo.owner_tags_on(nil, :locations) # => Ownerships equivalent to saying @some_photo.locations
+
 === Tag cloud calculations
 
 To construct tag clouds, the frequency of each tag needs to be calculated.