Better documentation for contributing / building etc

[arianvp]

@jvanbruegge noted they struggled to get things to build. I should spend more time explaining how it works and make sure it isn't actually broken

[jvanbruegge]

Yeah, and as said, I am using Arch which does not really work well with nix. Having a docker container that I could just mount the project folder into that has all the nix stuff included would allow me too to build and test everything