Add section on insecure-registry

Wasted a whole bunch of time dealing with VPN and other issues, but the real issue was this.

Originally posted by @mhamrah here: https://github.com/docker/docker/issues/8887#issuecomment-61864331
Also, not sure you need to delete the old image, that trashes all your local images so its not ideal. Just appending to `/var/lib/boot2docker/profile` and restarting the daemon works for me.