Users can do this themselves by using the ${NAME} field.
Hard coding behaviour of these three variables was a mistake, and this
is a lot more flexible. I could add back the variables and don't document them
if people think someone has used them
BindTo=docker.service ensures, that the service is stopped or restarted
whenever docker is. This is more sane behavior if no docker restart policy is
given (i.e. --restart=always).
