[Feature] Dockerize this app

[JAG-010]

This application has all potential to be dockerized. If it was not a WIP, I can work on it and update.

[ondras]

Please feel free to send a MR with a Dockerfile. I would not say that the app is WIP, it is regularly used (incl. the github-hosted version).

I am not that much into Docker (the hosted version is happily using GitHub Pages static hosting) and my time is rather limited, so I would gladly accept this as a contribution.

[JAG-010]

Sure, Thanks. I will work on it and update.

[JAG-010]

I have create a PR

[Hobbabobba]

I created an image at https://hub.docker.com/repository/docker/bongobananne75/my-mindmap incl. docker-compose.yml for easier deployment.

Thanks for this great tool!