clarify verbiage

activemodel/README.rdoc

@@ -2,7 +2,7 @@
 
 Active Model provides a known set of interfaces for usage in model classes.
 They allow for Action Pack helpers to interact with non-Active Record models,
-for example. Active Model also helps building custom ORMs for use outside of
+for example. Active Model also helps with building custom ORMs for use outside of
 the Rails framework.
 
 Prior to Rails 3.0, if a plugin or gem developer wanted to have an object