Add Package to System

One way to add packages to NixOS is to add the required packages to the pkgs list in the /etc/nixos/configuration.nix as follows:

environment.systemPackages = with pkgs; [
  # Added line below to install vim
  vim
  findutils
  gnumake
  iputils
  jq
  nettools
  netcat
  rsync
];

Once the edit is made, then a rebuild of the system is required:

# nixos-rebuild switch