When installing nixos:

Don't forget you can access the nix installation manual by pressing ALT+F8

• follow the nix installation manual until step 10
• use nix-env -i git to get git in the shell
• clone this repository in /etc/nixos
• link configuration.nix to a known machine or create a new one
• run nixos-generate-configuration to have the hardware-configuration.nix generated.
• continue the nix installation manual