Fix showtopics option

Add a missing comment for showtopics default value.
Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>

src/samples/stdoutsub.c

@@ -30,6 +30,7 @@
 	--qos 2
 	--delimiter \n
 	--clientid stdout_subscriber
+	--showtopics off
 	
 	--userid none
 	--password none

src/samples/stdoutsuba.c

@@ -30,6 +30,7 @@
 	--qos 2
 	--delimiter \n
 	--clientid stdout_subscriber
+	--showtopics off
 	
 	--userid none
 	--password none