Documentation for multiple DB's via docker-compose.yml

Hi, I was just curious is there was any plan for documentation regarding multiple `postgres` instance's connecting to a single `graphql-engine` instance via docker-compose, and what the environement variable, namely `HASURA_GRAPHQL_DATABASE_URL` would look like, or how it would be handled.

... or if connecting the console/api/cli methods are preferred over this type of approach.