Updated docs

docs/guide/defining-documents.rst

@@ -533,10 +533,15 @@ convenient and efficient retrieval of related documents::
     class Page(Document):
         title = StringField(max_length=200, required=True)
 
+        meta = {'allow_inheritance': True}
+
     # Also stored in the collection named 'page'
     class DatedPage(Page):
         date = DateTimeField()
 
+.. note:: From 0.7 onwards you must declare `allow_inheritance` in the document
+meta.
+
 Working with existing data
 --------------------------
 To enable correct retrieval of documents involved in this kind of heirarchy,