doc: mvn docker.registry

[patriknw]

When using mvn -X -Ddocker.registry=<username> it shows

The push refers to repository [docker.io/patriknw/restaurant-drone-deliveries-service]

otherwise it will be double restaurant-drone-deliveries-service

There is something that has changed with how credentials are retrieved. Seems like the default docker login that stores in ~/.docker/config.json doesn't work with the maven plugin any more. I could get it working in another way, but the recommended credsStore doesn't work for me. See

• https://docs.docker.com/engine/reference/commandline/login/#credentials-store
• https://dmp.fabric8.io/#authentication