Docker Rocker

Add Dockerfile and update Readme with instructions on how to run it.

If you, Christian, create now a repository named `netz98/docker-ui` on [https://registry.hub.docker.com/](https://registry.hub.docker.com/) then you can spare the build command and directly run:

```
docker run -d -p 8090:8090 -v /var/run/docker.sock:/var/run/docker.sock n98/docker-ui
```

Docker will then automatically pull the image from DockerHub which you have pushed before.

For each new release of docker-ui rebuild the image and push it to the DockerHub.

Port number of 8090? I have found it on Bondi Beach ;-)