Add Dockerfile

[Tailzip]

Add Dockerfile to be able to use tfjson binary using a Docker container.

Happy to create a PR if you want the image to be automatically published on the Docker Hub when CI passes :)

[palantirtech]

Thanks for your interest in palantir/tfjson, @Tailzip! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.