Update protobuf.md (#2949)

diff --git a/content/zh-cn/overview/mannual/java-sdk/reference-manual/serialization/protobuf.md b/content/zh-cn/overview/mannual/java-sdk/reference-manual/serialization/protobuf.md
index 6228d88..2ff703e 100644
--- a/content/zh-cn/overview/mannual/java-sdk/reference-manual/serialization/protobuf.md
+++ b/content/zh-cn/overview/mannual/java-sdk/reference-manual/serialization/protobuf.md
@@ -18,7 +18,16 @@
 
 ## 2 使用方式
 
-### 2.1 配置启用
+### 2.1 引入依赖
+```xml
+<dependency>
+    <groupId>org.apache.dubbo</groupId>
+    <artifactId>dubbo-serialization-protobuf</artifactId>
+    <version>2.7.23</version>
+</dependency>
+```
+
+### 2.2 配置启用
 
 
 ```yaml