script: Add explanatory comment to tc.sh

Author: dscotese

contrib/qos/tc.sh

@@ -16,7 +16,7 @@ LOCALNET_V4="192.168.0.0/16"
 #defines the IPv6 address space for which you wish to disable rate limiting
 LOCALNET_V6="fe80::/10"
 
-#delete existing rules
+#delete existing rules ('Error: Cannot delete qdisc with handle of zero.' means there weren't any.)
 tc qdisc del dev ${IF} root
 
 #add root class