Add DOCKERFILE

This adds a docker setup as in #1 to run the examples and some hints in the readme on how to use it.

It uses the "isolated" way to run GUI in docker containers described in http://wiki.ros.org/docker/Tutorials/GUI#The_isolated_way . I think it should be sufficiently secure. The only downside is that you have to change the DOCKERFILE if your user is not the primary user on your system.