video tutorial added

README.md

@@ -11,7 +11,7 @@ Gateway is a restful API gateway based on HTTP, which can be used as a unified A
 ## Tutorial
 A very detailed tutorial for beginners. [Link](./docs/tutorial.md) 
 Here is the corresponding video tutorial. 
-<iframe width="560" height="315" src="https://www.youtube.com/embed/2qMWmdcw7o4" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
+[![](https://img.youtube.com/vi/2qMWmdcw7o4/0.jpg)](https://www.youtube.com/watch?v=2qMWmdcw7o4)
 
 ## Attention
 Please make sure your Go version is 1.10 or above. Otherwise, **undefined "math/rand".Shuffle** error will occur when compiling. [StackOverFlow Link](https://stackoverflow.com/questions/52172794/getting-undefined-rand-shuffle-in-golang)