rfkill-udev: add license

pkgs/os-specific/linux/rfkill/udev.nix

@@ -47,9 +47,10 @@ in stdenv.mkDerivation {
     cp ${rfkillHook} "$out/bin/rfkill-hook.sh"
   '';
 
-  meta = {
+  meta = with stdenv.lib; {
     homepage = "http://wireless.kernel.org/en/users/Documentation/rfkill";
     description = "Rules+hook for udev to catch rfkill state changes";
-    platforms = stdenv.lib.platforms.linux;
+    platforms = platforms.linux;
+    license = licenses.mit;
   };
 }