First, install nix from here.
Second, install home-manager from here.
Clone this repository to ~/.config/home-manager.
Allow experimental features:
mkdir -p ~/.config/nix
cat <<EOF >> ~/.config/nix/nix.conf
experimental-features = nix-command flakes
EOF
Install by running:
home-manager switch
For completion in neovim with Codeium, start nvim and run Codeium Auth to import a token.