Added Sphinx autodoc file for celery.backends.mongodb

docs/reference/celery.backends.mongodb.rst

@@ -0,0 +1,8 @@
+============================================
+ Backend: MongoDB - celery.backends.mongodb
+============================================
+
+.. currentmodule:: celery.backends.mongodb
+
+.. automodule:: celery.backends.mongodb
+    :members:

docs/reference/index.rst

@@ -34,6 +34,7 @@
     celery.backends.database
     celery.backends.cache
     celery.backends.amqp
+    celery.backends.mongodb
     celery.backends.tyrant
     celery.conf
     celery.datastructures