package/setserial: 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: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/setserial/Config.in

@@ -4,3 +4,5 @@ config BR2_PACKAGE_SETSERIAL
 	depends on BR2_USE_MMU
 	help
 	  Setserial : configuration of serial ports
+
+	  http://setserial.sourceforge.net/