Add flake.nix for nixos

[benjujo]

I make this flake for nixos with flakes support to get the drivers in NixOS system.
It works adding inputs.zj-58.url = github:klirichek/zj-58 to the flake en into the system configuration:

modules = [
  ...
  {
    services.printing = {
      enable = true;
      drivers = [ zj-58.packages.x86_64-linux.default ];
    };
  }
]
```