README: fix installations link for Mac OSX

    Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
Merge pull request #195 from proppy/patch-1

README: fix installations link for Mac OSX
Create driver model and refactor virtualbox dependencies into driver
Bring back explicit init command; add init flag to force auto initialize.