closes #854 clear up doc confusion on producer config

config.go

@@ -99,7 +99,10 @@ type Config struct {
 		Partitioner PartitionerConstructor
 
 		// Return specifies what channels will be populated. If they are set to true,
-		// you must read from the respective channels to prevent deadlock.
+		// you must read from the respective channels to prevent deadlock. If,
+		// however, this config is used to create a `SyncProducer`, both must be set
+		// to true and you shall not read from the channels since the producer does
+		// this internally.
 		Return struct {
 			// If enabled, successfully delivered messages will be returned on the
 			// Successes channel (default disabled).