Add CirrOS Docker Image

"CirrOS is a Tiny OS that specializes in running on a cloud."

This stackbrew image is maintained by Eric Windisch,
while CirrOS itself is maintained by Scott Moser.

More on CirrOS may be found on its launchpad page:
    https://launchpad.net/cirros
Merge pull request #26 from ewindisch/master

Add CirrOS Docker Image