please change "add it to the docker image registry." to "add it to the local image cache."

You've stumbled on an area where we didn't previously have a term, and I can see why you chose "registry" because a lot of the functionality is similar. But the [local image cache](https://botbot.me/freenode/docker-dev/msg/6989527/) is not a proper registry because it does not respond to the [Registry API](http://docs.docker.io/en/latest/api/registry_api/).