package/metacity: add an upstream URL to Config.in

Add an upstream URL to the help text in Config.in. This
addresses the 'Missing' URL status in the package stats
web page output.

Signed-off-by: Mark Corbin <mark@dibsco.co.uk>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/metacity/Config.in

@@ -14,3 +14,5 @@ config BR2_PACKAGE_METACITY
 	select BR2_PACKAGE_XLIB_LIBXFT
 	help
 	  Metacity is a window manager for the X Window System.
+
+	  https://wiki.gnome.org/Projects/Metacity