nixos/perlless: correct documented warning

nixos/modules/profiles/perlless.nix

@@ -1,8 +1,4 @@
-# WARNING: If you enable this profile, you will NOT be able to switch to a new
-# configuration and thus you will not be able to rebuild your system with
-# nixos-rebuild!
-
-{ lib, ... }:
+{ lib, pkgs, ... }:
 
 {
 
@@ -31,4 +27,8 @@
   # string "perl".
   system.forbiddenDependenciesRegexes = ["perl"];
 
+  # Re-add nixos-rebuild to the systemPackages that was removed by the
+  # `system.disableInstallerTools` option.
+  environment.systemPackages = [pkgs.nixos-rebuild];
+
 }