Provide Dockerfile build environment

[DerekV]

It might be nice for those who want to build themselves without having to install the dependencies (thoughtfully listed in the README), and who are Docker users, to have a Dockerfile that will provide a build environment.

For the way I am thinking it might be implemented, the only code to add would be a "Dockerfile" file and a special make target. The target would build the docker container environment, mount the current directly into it, and run make inside.

I can work on this and open a PR if it sounds useful.