Respond to CR.

// FREEBIE

SignalServiceKit/src/Messages/OWSReadReceiptManager.m

@@ -467,6 +467,8 @@ NSString *const OWSReadReceiptManagerAreReadReceiptsEnabled = @"areReadReceiptsE
     OWSAssert(message);
     OWSAssert(transaction);
 
+    // Use timestampForSorting which reflects local sort order, rather than timestamp
+    // which reflect sender time.
     [self markAsReadBeforeTimestamp:message.timestampForSorting
                              thread:message.thread
                            wasLocal:NO