Add documentation for docker

[jniles]

We need to add additional documentation now that we've merged the initial support for docker (#6229).

There are still some things that needs to done:

1. We need to have a better way of building the MySQL database. Currently, the user has to run yarn build:docker to create an initial database file to populate the database.
2. We should be using multi-stage builds to ensure that we only have build artifacts in a "build" image and then deploy the most minimal image one can think of.
3. We need documentation on how to deploy/run with docker & docker-compose.