NixOS modules

First, you need to add this project to your flake inputs:

{
    inputs = {
        nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
        bonfire.url = "github:L-Nafaryus/bonfire";
    };
    outputs = { nixpkgs, bonfire, ... }:
    { ... }
}

After, you can use in a NixOS configuration like so

{
    nixosConfigurations.foo = nixpkgs.lib.nixosSystem {
        system = "x86_64-linux";
        modules = [
            bonfire.nixosModules.bonfire
            # or default because bonfire is default module
            bonfire.nixosModules.default
            # or just standalone module 
            bonfire.nixosModules.bar
            ...
        ];
    };
}