add: Dockerfile for running in container

[dpezely]

Add Dockerfile for running within a container.

• Initially this is a draft PR because of issue #18
• This updates Node.js to latest stable because maintenance LTS and original versions produced many errors and warnings
• Additional instructions for Linux that puts user in more groups does NOT work within a Dockerfile
• Instructions are kept within the Dockerfile as comments to avoid polluting README, etc.
• See also draft PR for Vagrantfile for running within a guest VM