This reposity use chezmoi as the dotfile manager.
You can use sh -c "$(curl -fsLS get.chezmoi.io)" -- init --ssh --apply Undefined01 to install the configs.
For NixOS, run nix shell nixpkgs#{git,gnupg,chezmoi} -c chezmoi init --ssh --apply Undefined01. (Maybe with export {http_proxy,https_proxy,HTTP_PROXY,HTTPS_PROXY,all_proxy,ALL_PROXY}="http://<proxy>:<port>")