Mount home directory on VM

[bfirsh]

It is mounted at /Users/username on the VM so using volumes within your home directory more-or-less works seamlessly.

E.g. you could use this to mount some code you're working on inside a container:

$ docker run -v pwd:/opt myimage python app.py

[bfirsh]

Just going to merge this because it's getting some interest on HN!