Docker implementation for mongodb #13

[Christinarlong]

PR adds docker-compose file to run mongodb container and updates README for instructions on how to run (#13 ) References:

• https://hub.docker.com/_/mongo
• https://www.baeldung.com/linux/mongodb-as-docker-container

Notes:

• Requires Docker Desktop
• Database will be brought up on localhost:27017
• user/pass could be moved to an init or env file, I'm not sure what the standard practice for this is