Added page for documenting mongomock. Updated docs/guide/index.rst

docs/guide/mongomock.rst

@@ -0,0 +1,21 @@
+==============================
+Use mongomock for testing
+==============================
+
+`mongomock <https://github.com/vmalloc/mongomock/>`_ is a package to do just 
+what the name implies, mocking a mongo database.
+
+To use with mongoengine, simply specify mongomock when connecting with 
+mongoengine:
+
+.. code-block:: python
+
+    connect('mongoenginetest', host='mongomock://localhost')
+    conn = get_connection()
+
+or with an alias:
+
+.. code-block:: python
+
+    connect('mongoenginetest', host='mongomock://localhost', alias='testdb')
+    conn = get_connection('testdb)