Enhance README with PyMongo and Atlas links

Added information about PyMongo and MongoDB cluster setup.

Author: alexbevi

README.md

@@ -1,5 +1,7 @@
 # Django MongoDB Backend
 
+The Django MongoDB Backend is a Django database backend that uses [PyMongo](https://www.mongodb.com/docs/languages/python/pymongo-driver/current/) to connect to MongoDB.
+
 ## Documentation
 
 Documentation written in the style of MongoDB's documentation is available at
@@ -51,6 +53,9 @@ DATABASES = {
 }
 ```
 
+If you don't already have a MongoDB cluster, see the [getting started with Atlas](https://www.mongodb.com/docs/atlas/getting-started/) documentation
+to quickly and easily [deploy a free cluster](https://www.mongodb.com/docs/atlas/tutorial/deploy-free-tier-cluster/).
+
 ### Run the server
 
 To verify that you correctly configured your project, run the following command