Add Dockerfile and docker-compose setup

[croesnick]

Added a Dockerfile as well as a docker-compose config for a more convenient and isolated setup of Kanbanist. :)

[mwakerman]

If this is for development/testing (rather than deployment), can we mount the directory as a volume so that changes still trigger a hot reload?

[croesnick]

Very well spotted! 😊 The previous version indeed did bake in the code at build time which would not work with code changes/hot reloads as you asked for. I changed the code accordingly to mount in the local checkout so that yarn start should react to code changes as it would when starting it natively without docker.

[Wittionary]

The changes to README.md look okay to me. Can this be merged? @mwakerman @VikashKotharyWork