Imperative nixos container with autostart - how?

openmpi.nix

{
  autoStart = true;
  config = { config, pkgs, ... }: {
    environment.systemPackages = with pkgs; [
      # Shells:
      bash
      # For OpenMPI:
      binutils
      gfortran
      openmpi
    ];
    system.activationScripts = {
      text = ''
        ln -sfn /run/current-system/sw/bin/bash /bin/bash
        ln -sfn /run/current-system/sw/bin/mpi* /bin/
      '';
    };
  };
}