package/matchbox-lib: 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/matchbox-lib/Config.in

@@ -3,3 +3,5 @@ config BR2_PACKAGE_MATCHBOX_LIB
 	select BR2_PACKAGE_XLIB_LIBXEXT
 	help
 	  Matchbox common functionality library.
+
+	  http://git.yoctoproject.org/cgit/cgit.cgi/libmatchbox