[WIP/Do not merge]Add Dockerfile with README and config.js

The README includes documentation on how to build Ghost from master on
Docker. The config.js reads the necessary config from environment
variables.

I still struggle with the config.js. It keeps saying:

    ERROR: Cannot find the configuration for the current NODE_ENV
    NODE_ENV=production
    Ensure your config.js has a section for the current NODE_ENV value and is formatted properly.

Maybe someone point me in the right direction to fix that?