add Chinese version

docs/cn/Example_Delay.md

+# Schedule example
+
+### 1 启动消费者等待传入的订阅消息
+
+```java
+import org.apache.rocketmq.client.consumer.DefaultMQPushConsumer;
+import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyContext;
+import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyStatus;
+import org.apache.rocketmq.client.consumer.listener.MessageListenerConcurrently;
+import org.apache.rocketmq.common.message.MessageExt;
+import java.util.List;
+
+public class ScheduledMessageConsumer {
+
+    public static void main(String[] args) throws Exception {
+        // Instantiate message consumer
+        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("ExampleConsumer");
+        // Subscribe topics
+        consumer.subscribe("TestTopic", "*");
+        // Register message listener
+        consumer.registerMessageListener(new MessageListenerConcurrently() {
+            @Override
+            public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> messages, ConsumeConcurrentlyContext context) {
+                for (MessageExt message : messages) {
+                    // Print approximate delay time period
+                    System.out.println("Receive message[msgId=" + message.getMsgId() + "] "
+                                       + (System.currentTimeMillis() - message.getStoreTimestamp()) + "ms later");
+                }
+                return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
+            }
+        });
+        // Launch consumer
+        consumer.start();
+    }
+}
+```
+
+### 2 发送延迟消息 
+
+```java
+import org.apache.rocketmq.client.producer.DefaultMQProducer;
+import org.apache.rocketmq.common.message.Message;
+
+public class ScheduledMessageProducer {
+
+    public static void main(String[] args) throws Exception {
+        // Instantiate a producer to send scheduled messages
+        DefaultMQProducer producer = new DefaultMQProducer("ExampleProducerGroup");
+        // Launch producer
+        producer.start();
+        int totalMessagesToSend = 100;
+        for (int i = 0; i < totalMessagesToSend; i++) {
+            Message message = new Message("TestTopic", ("Hello scheduled message " + i).getBytes());
+            // This message will be delivered to consumer 10 seconds later.
+            message.setDelayTimeLevel(3);
+            // Send the message
+            producer.send(message);
+        }
+
+        // Shutdown producer after use.
+        producer.shutdown();
+    }
+
+}
+```
+
+### 3 确认
+
+您应该会看到消息在其存储时间后大约 10 秒被消耗。
+
+### 4 延迟消息的使用场景
+
+例如在电子商务中，如果提交订单，可以发送延迟消息，1小时后可以查看订单状态。 如果订单仍未付款，则可以取消订单并释放库存。
+
+### 5 使用延迟消息的限制
+
+```java 
+// org/apache/rocketmq/store/config/MessageStoreConfig.java
+
+private String messageDelayLevel = "1s 5s 10s 30s 1m 2m 3m 4m 5m 6m 7m 8m 9m 10m 20m 30m 1h 2h";
+```
+
+当前 RocketMQ 不支持任意时间的延迟。 生产者发送延迟消息前需要设置几个固定的延迟级别，分别对应1s到2h的1到18个延迟级，消息消费失败会进入延迟消息队列，消息发送时间与设置的延迟级别和重试次数有关。
+
+ See `SendMessageProcessor.java`