docs: improve bridge_mode description

apps/emqx_connector/i18n/emqx_connector_mqtt_schema.conf

@@ -114,9 +114,13 @@ topic filters for <code>remote.topic</code> of ingress connections."""
         desc {
             en: """If enable bridge mode.
 NOTE: This setting is only for MQTT protocol version older than 5.0, and the remote MQTT
-broker MUST support this feature."""
+broker MUST support this feature.
+If bridge_mode is set to true, the bridge will indicate to the remote broker that it is a bridge not an ordinary client.
+This means that loop detection will be more effective and that retained messages will be propagated correctly."""
             zh: """是否启用 Bridge Mode。
-注意：此设置只针对 MQTT 协议版本 < 5.0 有效，并且需要远程 MQTT Broker 支持 Bridge Mode。"""
+注意：此设置只针对 MQTT 协议版本 < 5.0 有效，并且需要远程 MQTT Broker 支持 Bridge Mode。
+如果设置为 true ，桥接会告诉远端服务器当前连接是一个桥接而不是一个普通的客户端。
+这意味着消息回环检测会更加高效，并且远端服务器收到的保留消息的标志位会透传给本地。"""
         }
         label {
             en: "Bridge Mode"