Updated docker-compose and README for new setup

[tenekev]

• Updated README.md install instructions to reflect the new Docker image.
• Updated the docker-compose.yml to reflect the new Docker image.
• Added a healthcheck to the database container to ensure it is running before the server starts. The server container would start before the database container, throwing 1-2 harmless connection error that were confusing people.
• Added some notes to the docker-compose.yml file. Ideally this should be expanded to a full markdown file with notes how to configure the containers but I think it's still too early to delve into changing details.