Dockerize!

This turned out to be easier than expected. Assuming users only interact with Mimic through the REST API, this is sufficient.

I added documentation on how to use this to the README. I figured you would probably want to keep the existing instructions as the default.
I think for a one-off configuration like this, we may want to recommend a command line that will clean up after itself, such as `docker run --rm=true --restart=no -p 8900:8900 mimic`.