Added VirtualBox instructions to quickstart.

[saintograph]

VirtualBox can be useful for developing with Conda or Jupyter Notebook in an isolated environment.

[anoff]

To isolate the environments they are all bundled as docker containers.

I appreciate the effort but I would not incorporate these instructions in the OM quickstart. They are not specific to OM itself and only show how to get VirtualBox setup. If this is necessary I'd rather link to virtualisation solutions. But imo every developer should know for themselves how they want to do their local development.

edit: my personal preference to keep python development clean is to use conda environments or virtualenv

/cc @cereallarceny @kevinahuber

[iamtrask]

Ah, so I agree with @anoff but mostly that this is the right content in the wrong place. @winfredselwyn , could we move this to a file in our "contributing" folder specifically focused around virtualbox?

[saintograph]

Will do @anoff @iamtrask.