Adding docker-compose.yml together with associated changes

README.md

 # Introduction to MongoDB
 
-An introduction to the MongoDB NoSQL database using the Python interface.
+An introduction to the MongoDB NoSQL database using the `pymongo` Python module.
+
+* Documentation is given in [doc/introduction-to-mongo.pdf](doc/introduction-to-mongo.pdf).
+* Example programs are given in [python/](python/).
+* The `docker-compose.yml` file can be used with [docker compose](https://docs.docker.com/compose/) to start MongoDB locally.
+
+```bash
+# Start the MongoDB server.
+docker compose up
+
+# Press ctrl-c to stop the running server.
+
+# Remove the mongodb container.
+docker compose down --rmi local
+
+# Remove the mongodb image from the local PC.
+docker compose down --rmi all
+```
+
+  
\ No newline at end of file

python/mongo_connect.py

@@ -13,8 +13,8 @@ def get_client():
 
     server = os.getenv('MONGODB_SERVER', 'localhost')
     port_str = os.getenv('MONGODB_PORT', '27017')
-    username = os.getenv('MONGODB_USERNAME', '')
-    password = os.getenv('MONGODB_PASSWD', '')
+    username = os.getenv('MONGODB_USERNAME', 'root')
+    password = os.getenv('MONGODB_PASSWD', 'example')
 
     # The port number should be an integer.
     try: