libppd: add meta attribute set

pkgs/by-name/li/libppd/package.nix

···
   cups,
   fetchFromGitHub,
   ghostscript,
+  lib,
   libcupsfilters,
   libz,
   mupdf,
···
     "CUPS_DATADIR=$(out)/share/cups"
     "CUPS_SERVERROOT=$(out)/etc/cups"
   ];
+
+  meta = {
+    description = "Library designed to support legacy printer drivers by handling PostScript Printer Description (PPD) file";
+    homepage = "https://github.com/OpenPrinting/libppd";
+    license = lib.licenses.asl20;
+    platforms = lib.platforms.linux;
+  };
 }