fix tcb example

tcb/README.md

@@ -23,7 +23,7 @@ wcTcb := wc.GetTcb()
 ### 举例
 #### 触发云函数
 ```golang
-res, err := wcTcb.UploadFile("test-6ku2s", "golang.png")
+res, err := wcTcb.InvokeCloudFunction("test-xxxx", "add", `{"a":1,"b":2}`)
 if err != nil {
     panic(err)
 }