NixOS/nixpkgs ? reverse-engineered prompt

Build me a Nix based package collection and Linux system configuration repo, like a small practical version of Nixpkgs and NixOS.

I want users to be able to define software packages in Nix, install them with the Nix package manager, and use the same repo to describe NixOS system options and modules. Please include clear manuals or getting started docs for installing packages, writing simple package definitions, configuring a NixOS machine, and contributing changes through GitHub.

Set it up so packages and system configs can be built and tested automatically, with a place for maintainers, contributor guidance, licensing notes, and community links. It should feel organized enough that lots of people could add packages over time without it becoming messy.

Keep the first version simple but real, with a few example packages and modules that actually build. Look up current Nix and NixOS docs online if you need to.