docs(pubsub): fix comments on message for exactly once delivery
Fixes
@@ -37,8 +37,10 @@ import (
//
// If using exactly once delivery, you should call Message.AckWithResult and
// Message.NackWithResult instead. These methods will return an AckResult,
-// which you should wait on to obtain the status of the Ack/Nack to ensure
-// these were properly processed by the server. If not,
+// which tracks the state of acknowledgement operation. If the AckResult returns
+// successful, the message is guaranteed NOT to be re-delivered. Otherwise,
+// the AckResult will return an error with more details about the failure
+// and the message may be re-delivered.
type Message = ipubsub.Message
// msgAckHandler performs a safe cast of the message's ack handler to psAckHandler.
