english version and chinese version

docs/cn/getting_started.md

@@ -1,3 +1,5 @@
+[English version](../en/getting_started.md)
+
 # 构建
 
 brpc鼓励静态链接依赖，以便于每个运行brpc服务的机器不必再安装依赖。

docs/en/getting_started.md

@@ -1,3 +1,5 @@
+[中文版](../cn/getting_started.md)
+
 # BUILD
 
 brpc prefers static linkages of deps, so that they don't have to be installed on every machine running the app.