Add docker-compose.yml

[jsfan]

The docker-compose.yml file should configure a stack which contains the app, an NginX reverse proxy and a PostgreSQL server.

The database needs to be kept on a volume mounted from the host system's disk.
Ideally, the NginX reverse proxy should be configured for HTTPS and read its key and certificate from a mount on the host system. This may require another Dockerfile and possibly a build script to build Docker images and create a self-signed key pair by default.

The docker-compose.yml should be suitable for the docker stack command rather than docker-compose.

[jsfan]

https://docs.docker.com/compose/compose-file/

[jsfan]

https://docs.docker.com/compose/

[jsfan]

I'll leave this open for now. The init script doesn't bring up the app container. However, without the app container Nginx will flap and the certificate never issued.

It's possible to work around that to run the init script until it fails, bring up the stack with the self-signed certificate and then re-run the init script while the stack is up.