Add description and license to HashDiff

pkgs/top-level/perl-packages.nix

@@ -6799,6 +6799,11 @@ let
       sha256 = "1ig0l859gq00k0r9l85274r2lbvwl7wsndcy52c0m3y9isilm6mw";
     };
     propagatedBuildInputs = [ HashMerge ];
+
+    meta = {
+      license = with stdenv.lib.licenses; [ artistic1 ];
+      description = "Return difference between two hashes as a hash";
+    };
   };
 
   HashFlatten = buildPerlPackage rec {