Tweak some docs

Clarify the behaviour of `WaitForAll`. Also fix some spelling/punctuation around
`HighWaterMarks` while I'm looking at the docs.

consumer.go

@@ -63,8 +63,8 @@ type Consumer interface {
 	// or OffsetOldest
 	ConsumePartition(topic string, partition int32, offset int64) (PartitionConsumer, error)
 
-	// HighWaterMarks returns the current high water marks for each topic and partition
-	// Consistency between partitions is not garanteed since high water marks are updated separately.
+	// HighWaterMarks returns the current high water marks for each topic and partition.
+	// Consistency between partitions is not guaranteed since high water marks are updated separately.
 	HighWaterMarks() map[string]map[int32]int64
 
 	// Close shuts down the consumer. It must be called after all child

produce_request.go

@@ -14,7 +14,9 @@ const (
 	NoResponse RequiredAcks = 0
 	// WaitForLocal waits for only the local commit to succeed before responding.
 	WaitForLocal RequiredAcks = 1
-	// WaitForAll waits for all replicas to commit before responding.
+	// WaitForAll waits for all in-sync replicas to commit before responding.
+	// The minimum number of in-sync replicas is configured on the broker via
+	// the `min.insync.replicas` configuration key.
 	WaitForAll RequiredAcks = -1
 )