Possibly adding an option to use `stenv` in a docker container

[amanchokshi]

Hey guys, just starting to play with stenv and thought it may be a good idea to give the people the option to play with the environment through a docker container. I think astroconda used to have something similar, or at least a build environment container.

I've made something that may work: github.com/amanchokshi/stenv-docker which also has jupyter notebook and jupyterlab functionality built in.

Cheers, Aman