corefonts: add meta and mark as unfree

See e.g. https://sourceforge.net/p/corefonts/bugs/6/

pkgs/data/fonts/corefonts/default.nix

@@ -1,4 +1,4 @@
-{stdenv, fetchurl, cabextract}:
+{ stdenv, fetchurl, cabextract }:
 
 let
 
@@ -59,7 +59,11 @@ stdenv.mkDerivation {
     done
   '';
 
-  meta = {
+  meta = with stdenv.lib; {
+    homepage = "http://corefonts.sourceforge.net/";
+    description = "Microsoft's TrueType core fonts for the Web";
+    platforms = platforms.all;
+    licenses = licenses.unfreeRedistributable;
     # Set a non-zero priority to allow easy overriding of the
     # fontconfig configuration files.
     priority = 5;