lkl: add note for future update attempts

stdenv.mkDerivation rec {

  pname = "lkl";

  # NOTE: pinned to the last known version that doesn't have a hang in cptofs.

  # Please verify `nix build -f nixos/release-combined.nix nixos.ova` works

  # before attempting to update again.

  # ref: https://github.com/NixOS/nixpkgs/pull/219434

  version = "2022-08-08";

  outputs = [ "dev" "lib" "out" ];