package/mrouted: update description a bit, mention oper. requirement

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/mrouted/Config.in

@@ -3,5 +3,11 @@ config BR2_PACKAGE_MROUTED
 	depends on BR2_USE_MMU # fork()
 	help
 	  An implementation of the DVMRP multicast routing protocol.
+	  Unlike PIM a DVMRP router has a distance vector protocol (like
+	  RIP) built-in to figure out the reverse-path to the multicast
+	  source. This package comes with mrouted and mroutectl.  Where
+	  the latter is used to query status and control operation.
+
+	  Note: at least two interfaces with MULTICAST flag is requried.
 
 	  http://github.com/troglobit/mrouted