Add Docker support

[pataquets]

Add Dockerfile to enable image building. Useful for development and tests under Docker workflow.
Using the official Python image, :2 tag. More info at https://hub.docker.com/_/python/

Just adding files, setting working dir and running install.

Build:

$ docker build -t elasticstat .

Run:

$ docker run --rm -it elasticstat [options...]

FYI, there's a still quicker to test, already built image on my Docker Hub. Test it by running:

$ docker run --rm -it pataquets/elasticstat-src [options...]

Should stop by CTRL+C'ing it.
If no options given, assume --helpto avoid any error message.

Optional improvement to come (maybe in another issue):

• Create an 'official', based on your repo, automated build at Docker Hub for the image: https://docs.docker.com/docker-hub/builds/ . Just requires a free Docker Hub account and a following a quick 'Create automated build' process. I'll be happy to help on it, if needed. Useful as an easy direct-from-source (branches and tags) distribution method and for having a 'daily' build from source on each commit.

[paulrossmeier]

Hello pataquets,

I wanted to thank you for your contribution - we are reviewing and will update accordingly.

Paul Rossmeier

[paulrossmeier]

I have tested this and works fine - I need to get a reviewer to approve the merge

Paul Rossmeier