Zero to Nix introduces Nix, not NixOS the operating system. So, there's not really a need for screen shots as Zero to Nix it teaching how best to install and use Nix on any Linux or macOS. For that, code snippets are convenient I think.
From the questions in the parent post I wonder if it would be good to have a clear definition of what Nix is, what NixOS is, how they're different, and when to use each? Could just be a short paragraph, but if the site is for people just starting out it might be helpful...