Clarify flow control parameter descriptions
Clarify flow control parameter descriptions

kamalaboulhosn/pubsub,kamalaboulhosn/pubsub,kamalaboulhosn/pubsub,kamalaboulhosn/pubsub,GoogleCloudPlatform/pubsub,kamalaboulhosn/pubsub,GoogleCloudPlatform/pubsub,GoogleCloudPlatform/pubsub,GoogleCloudPlatform/pubsub,GoogleCloudPlatform/pubsub