Added indexes and Django use to docs

mongoengine/document.py

@@ -44,6 +44,11 @@ class Document(BaseDocument):
     maximum size of the collection in bytes. If :attr:`max_size` is not 
     specified and :attr:`max_documents` is, :attr:`max_size` defaults to 
     10000000 bytes (10MB).
+
+    Indexes may be created by specifying :attr:`indexes` in the :attr:`meta`
+    dictionary. The value should be a list of field names or tuples of field 
+    names. Index direction may be specified by prefixing the field names with
+    a **+** or **-** sign.
     """
 
     __metaclass__ = TopLevelDocumentMetaclass