Added indexes and Django use to docs

docs/userguide.rst

@@ -168,6 +168,22 @@ The following example shows a :class:`Log` document that will be limited to
         ip_address = StringField()
         meta = {'max_documents': 1000, 'max_size': 2000000}
 
+Indexes
+-------
+You can specify indexes on collections to make querying faster. This is done
+by creating a list of index specifications called :attr:`indexes` in the
+:attr:`~Document.meta` dictionary, where an index specification may either be
+a single field name, or a tuple containing multiple field names. A direction
+may be specified on fields by prefixing the field name with a **+** or a **-**
+sign. Note that direction only matters on multi-field indexes. ::
+
+    class Page(Document):
+        title = StringField()
+        rating = StringField()
+        meta = {
+            'indexes': ['title', ('title', '-rating')]
+        }
+
 Document inheritance
 --------------------
 To create a specialised type of a :class:`~mongoengine.Document` you have