add Dockerfile and adjust readme to reflect a quick start

[kniec]

Took the freedom to add a Dockerfile and adjusting the readme to have a quick start (#11).

[yuvipanda]

Thank you for working on this, @kniec!

We currently rely on the 'apt.txt' and 'environment.yml' to do the same thing you're doing in the Dockerfile - those work on mybinder.org with repo2docker. In general I prefer that, especially over inheriting from a heavy docker image like datascience-notebook.

We could add this as an example of 'if you want to build your own Dockerfile from jupyter-stacks' or build a 'minimal Dockerfile' version. What do you think?

[kniec]

I changed the base image to a smaller (220MB) version of the jupyter notebook.

What would be the minimal version of the notebook you would see possible?

[yuvipanda]

This is more useful than what we have now, so <3 thanks @kniec! Apologies for the delayed merge.