Lost order in db when restart container

[alessiofx]

When you restart the container all the orders on the database are lost.
You can fix this problem.

[fabioberger]

You can do this by mounting a volume to the Docker container where the database.sql file is stored so that it persists across container re-starts. We can add instructions to the README on how to do this. Thanks for the suggestion.

[dekz]

This will be possible once #65 is merged. Currently you can mount from local but not allocate a persistent volume.

[dekz]

A Docker volume can now be attached to the backend to allow for persistent orders through restarts

backend:
    ...
    volumes:
      - backend-database:/usr/app/src/db