with yadm:
    https://github.com/jluttine/nixos-configuration

https://discourse.nixos.org/t/github-strategies-for-configuration-nix/1983

... latest comment is cool ...
Here’s what /etc/nixos/configuration.nix looks like on one of my machines.

{ config, pkgs, options, ... }:

let hostname="wombat9000";
in
{
  networking.hostName = hostname;

  imports =
    [ # Include the results of the hardware scan.
      /etc/nixos/hardware-configuration.nix
      (/home/amy/dotWombat/nixos + "/${hostname}.nix")
      /home/amy/dotWombat/nixos/base.nix
      /home/amy/dotWombat/nixos/locale.nix
      /home/amy/dotWombat/nixos/xserver.nix
      /home/amy/dotWombat/nixos/python2.nix
      /home/amy/dotWombat/nixos/python3.nix
      /home/amy/dotWombat/nixos/R.nix
      /home/amy/dotWombat/nixos/packages.nix
    ];
}

and even better
https://www.reddit.com/r/NixOS/comments/6zn5tv/manage_nixos_config_from_git_without_having_to/
nix.nixPath = [
  "nixpkgs=/home/user/src/nixpkgs"
  # "nixos-config=/etc/nixos/configuration.nix"
  "nixos-config=/home/user/src/nixos/configuration.nix"
];

I chown /etc/nixos to my user, and have the .git directory in there.

Rather than messing around with /etc I prefer to:
    $ nixos-rebuild switch -I nixos-config=path/to/configuration.nix 

with home-manager
    https://hugoreeves.com/posts/2019/nix-home/
    cd ~/.config/nixpkgs; git pull; home-manager switch
    https://github.com/HugoReeves/nix-home/
    Let's start with an entry point,
        ~/.config/nixpkgs/home.nix,
    this is the file that home-manager uses by default as it's entry point.