meas: Add VTY documentation for the measurement commands

Document the parameters that can be passed on.
diff --git a/openbsc/src/libmsc/vty_interface_layer3.c b/openbsc/src/libmsc/vty_interface_layer3.c
index 97a2a09..4659355 100644
--- a/openbsc/src/libmsc/vty_interface_layer3.c
+++ b/openbsc/src/libmsc/vty_interface_layer3.c
@@ -1007,9 +1007,10 @@
 	return CMD_SUCCESS;
 }
 
+#define MEAS_STR "Measurement export related\n"
 DEFUN(mnccint_meas_feed, mnccint_meas_feed_cmd,
 	"meas-feed destination ADDR <0-65535>",
-	"FIXME")
+	MEAS_STR "destination\n" "address or hostname\n" "port number\n")
 {
 	int rc;
 
@@ -1022,7 +1023,7 @@
 
 DEFUN(meas_feed_scenario, meas_feed_scenario_cmd,
 	"meas-feed scenario NAME",
-	"FIXME")
+	MEAS_STR "scenario\n" "Name up to 31 characters included in report\n")
 {
 	meas_feed_scenario_set(argv[0]);