fix(README): add apigateway endpoint example (#20129)

pkg/mcclient/README.md

@@ -58,3 +58,45 @@ func main() {
 	fmt.Printf("%s", jsonutils.Marshal(result).PrettyString())
 }
 ```
+
+使用统一API入口调用
+文档说明: https://www.cloudpods.org/docs/development/apisdk/apigateway/
+
+```golang
+package main
+
+import (
+	"context"
+	"fmt"
+
+	"yunion.io/x/jsonutils"
+
+	"yunion.io/x/onecloud/pkg/mcclient"
+	modules "yunion.io/x/onecloud/pkg/mcclient/modules/compute"
+)
+
+func main() {
+	client := mcclient.NewClient("https://10.127.100.2/api/s/identity/v3", // 注意此地址不带端口
+		60,
+		true,
+		true,
+		"",
+		"")
+	token, err := client.Authenticate("sysadmin", "7AQMP9H2umQvbxxx", "Default", "system", "Default")
+	if err != nil {
+		panic(err)
+	}
+	s := client.NewSession(context.Background(),
+		"region0",
+		"",
+		"apigateway", // 注意此endpoint类型
+		token,
+		)
+
+	result, err := modules.Servers.List(s, nil)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("%s", jsonutils.Marshal(result).PrettyString())
+}
+```