Add link to Docker images

[lorddaedra]

Hello, @chriskuehl !

Thanks for your work.

I've just created container images with your package. It can be useful too for some environments.

https://github.com/backupner/dumb-pypi-image

[lorddaedra]

List of available image tags: https://hub.docker.com/r/backupner/dumb-pypi/tags

[Anthony Sottile]

#85 (comment)