Add Message docs

docs/en/_sidebar.md

@@ -1,6 +1,9 @@
 * MQTT Coroutine Client
     * [Client API](en/client)
 
+* MQTT Server
+  * [Message API](en/message)
+
 * MQTT Protocol Analysis
     * [Protocol API](en/protocol)
 

docs/en/message.md

@@ -0,0 +1,32 @@
+# Message API
+
+It is mainly convenient for replying to the ACK on the other side in the Server.
+
+## Usage examples
+
+```php
+use Simps\MQTT\Message\SubAck;
+use Simps\MQTT\Protocol\ProtocolInterface;
+
+$codes = [0];
+$message_id = 8520;
+
+$ack = new SubAck();
+$ack->setCodes($codes)
+    ->setMessageId($message_id);
+
+$ack_data = $ack->getContents();
+$ack_data = (string) $ack;
+
+// MQTT5
+$ack->setProtocolLevel(ProtocolInterface::MQTT_PROTOCOL_LEVEL_5_0)
+    ->setCodes($codes)
+    ->setMessageId($message_id)
+    ->setProperties([
+        'will_delay_interval' => 60,
+        'message_expiry_interval' => 60,
+    ]);
+
+$ack_data = $ack->getContents();
+$ack_data = (string) $ack;
+```

docs/zh-cn/_sidebar.md

@@ -1,6 +1,9 @@
 * MQTT 协程客户端
     * [Client API](zh-cn/client)
 
+* MQTT Server
+  * [Message API](zh-cn/message)
+
 * MQTT 协议解析
     * [Protocol API](zh-cn/protocol)
 

docs/zh-cn/message.md

@@ -0,0 +1,32 @@
+# Message API
+
+主要方便用于在 Server 中回复对端 ACK。
+
+## 使用示例
+
+```php
+use Simps\MQTT\Message\SubAck;
+use Simps\MQTT\Protocol\ProtocolInterface;
+
+$codes = [0];
+$message_id = 8520;
+
+$ack = new SubAck();
+$ack->setCodes($codes)
+    ->setMessageId($message_id);
+
+$ack_data = $ack->getContents();
+$ack_data = (string) $ack;
+
+// MQTT5
+$ack->setProtocolLevel(ProtocolInterface::MQTT_PROTOCOL_LEVEL_5_0)
+    ->setCodes($codes)
+    ->setMessageId($message_id)
+    ->setProperties([
+        'will_delay_interval' => 60,
+        'message_expiry_interval' => 60,
+    ]);
+
+$ack_data = $ack->getContents();
+$ack_data = (string) $ack;
+```