Motivation for this change

I wanted to use auto-cpufreq and so do others AdnanHodzic/auto-cpufreq#130

Things done

Create the auto-cpufreq package and add myself to maintainers

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

There really needs to be a NixOS module, but I will work on it after this gets merged.
Here is a temporary solution to get the systemd service:

environment.systemPackages = [ pkgs.auto-cpufreq ];

systemd.services.auto-cpufreq = {
    description = "auto-cpufreq - Automatic CPU speed & power optimizer for Linux";
    after = [ "network.target" "network-online.target" ];
    unitConfig.ConditionPathExists = "/var/log/auto-cpufreq.log";
    path = with pkgs; [ ncurses bash ];
    serviceConfig = {
      Type = "simple";
      User = "root";
      ExecStart = "${pkgs.auto-cpufreq}/bin/auto-cpufreq --daemon";
      StandardOutput = "append:/var/log/auto-cpufreq.log";
    };
    wantedBy = [ "multi-user.target" ];
  };
};