[skip ci]Add comment for rocksmq reader (#13012)

Signed-off-by: fishpenguin <kun.yu@zilliz.com>

internal/util/rocksmq/client/rocksmq/reader_impl.go

@@ -79,6 +79,7 @@ func (r *reader) Close() {
 	r.c.server.CloseReader(r.topic, r.name)
 }
 
+// Seek seek the reader to the position of message id
 func (r *reader) Seek(msgID UniqueID) error { //nolint:govet
 	r.c.server.ReaderSeek(r.topic, r.name, msgID)
 	return nil