add Docker.ignore

[kobiam]

Reasons for making this change:

adding Dockerfile for docker users

Links to documentation supporting these rule changes:

https://docs.docker.com/engine/reference/builder/#dockerignore-file

If this is a new template:

docker.com

[polarathene]

You linked to docs about the .dockerignore file.. That is not a .gitignore file, it serves a different purpose, it's for ignoring files when building Docker images rather than files to ignore when working with git..

This PR should be rejected. You don't appear to understand what you're contributing.

[shiftkey]

@kobiam while .dockerignore looks similar to a .gitignore file, their use cases are different enough and a potential source of confusion that I think this should not be added.

Without more information about what this template represents and why it's important, I cannot take in this PR.