Install NixOS as normal
Copy id_rsa and id_rsa.pub - or generate them and add to GitHub.
git config --global user.name "Matt Rose"
git config --global user.email "matt@glaikit.co.uk"
Then use git to grab the config
mkdir ~/dotfiles
cd ~/dotfiles
git clone git@github.com:boswall/nixos.git
cd nixos
Enjoy!