Docker container build: Using `/root` as the work dir is not advised

[samip5]

Hi there,

I was looking at the Dockerfile and noticed that the app root is at /root, I'm not exactly sure why one would think of putting it there, but that seems like not the greatest design decisions, so it should probably be fixed. I'm not sure if that will actually prevent the container from working as non-root.

Please instead move it to eg /app and just create the directory before changing work dir there.