Docs: Added link to tutorial on code splitting (#2427)

* Adding link to tutorial on code splitting

Link to tutorial on Code Splitting with React Router

* Update README.md

packages/react-scripts/template/README.md

@@ -377,6 +377,10 @@ This will make `moduleA.js` and all its unique dependencies as a separate chunk
 
 You can also use it with `async` / `await` syntax if you prefer it.
 
+### With React Router
+
+If you are using React Router check out [this tutorial](http://serverless-stack.com/chapters/code-splitting-in-create-react-app.html) on how to use code splitting with it. You can find the companion GitHub repository [here](https://github.com/AnomalyInnovations/serverless-stack-demo-client/tree/code-splitting-in-create-react-app).
+
 ## Adding a Stylesheet
 
 This project setup uses [Webpack](https://webpack.js.org/) for handling all assets. Webpack offers a custom way of “extending” the concept of `import` beyond JavaScript. To express that a JavaScript file depends on a CSS file, you need to **import the CSS from the JavaScript file**: