libosip2: document project URL in menuconfig

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/libosip2/Config.in

@@ -7,3 +7,5 @@ config BR2_PACKAGE_LIBOSIP2
 	  control SIP based sessions in their applications.
 	  SIP is a open standard replacement from IETF for H323.
 
+	  http://www.gnu.org/software/osip/
+