Add Dockerfile to construct a docker image

Signed-off-by: Silvio Fricke <silvio.fricke@gmail.com>
dockerfile: add README.md

Signed-off-by: Silvio Fricke <silvio.fricke@gmail.com>
dockerfile: readme: use privileged docker process

We use kvm in the container so we need access to the hosts kvm subsystem,
and that is only accessible with the option --privileged.

Signed-off-by: Silvio Fricke <silvio.fricke@gmail.com>