nix-shell is an undocumented dependency

[acron0]

README doesn't mention this dependency which is a bit irritating.

I am trying to use this tool to build nixOS boxes because my host machine will not install nix and nix-shell...so having a dependency on nix-shell makes it unusable for me, unfortunately.

[jvcarli]

Hi @acron0, I've fixed this on my fork: https://github.com/jvcarli/nixbox. The only required dependencies now are ruby and packer. It was tested on macOS Big Sur.