Added Dockerfile and documentation

[qdm12]

• Final image size of 11.8MB based on Docker Scratch (empty image, no OS)
• Multi stage build for a smaller image size and faster rebuilds
• Docker build arguments to define node, go and alpine versions
• Dockerfile org.opencontainers.image style labels
• HTTP server based on a statically built Go binary HTTP server (high performance, small and one line in Dockerfile)
• Runs as user ID 1000 without root, for security purposes

[qdm12]

Just noticed I forgot to remove my email address from the Dockerfile as author org.opencontainers.image.authors you may want to add yours or change mine to yours if you want. I don't mind of course, but you're more the author than me!