Move the Dockerfile to the top level

[Zarquan]

Given that the whole purpose of this project is to create a Docker container, it would make sense to move the Dockerfile to the top level directory.

[Zarquan]

This should solve the problem reported by the automated build:

    buildx call failed with: error: failed to solve: failed to read dockerfile: open /tmp/buildkit-mount011227109/Dockerfile: no such file or directory

[pahjbo]

possibly - the alternative seems to be to use the context parameter on the action https://github.com/docker/build-push-action#path-context