It's a simple docker image to run your mrtg.
you will need a mrtg.cfg file (hint, run docker exec and play with cfgmaker)
The collected data goes to /mrtg_data in the container and you probably want to preserve is between restarts
So run it like:
$ docker run -d -t -v /path/to/my/data:/mrtg_data/ -v /path/to/cfg/mrtg.cfg:/etc/mrtg.cfg cityhawk/mrtg
Then serve the /path/to/my/data with the webserver of your choice. I'm running nginx:alpine like:
$ docker run -d -t -p 9080:80 -v /path/to/my/data:/usr/share/nginx/html nginx:alpine