kgpg: update description to reflect gnupg

pkgs/applications/kde/kgpg.nix

···
   '';
   meta = {
     homepage = "https://apps.kde.org/kgpg/";
-    description = "Encryption tool";
+    description = "A KDE based interface for GnuPG, a powerful encryption utility";
     license = [ lib.licenses.gpl2 ];
     maintainers = [ lib.maintainers.ttuegel ];
   };