Move code splitting to its own file

docusaurus/docs/code-splitting.md

@@ -0,0 +1,56 @@
+---
+id: code-splitting
+title: Code Splitting
+---
+
+Instead of downloading the entire app before users can use it, code splitting allows you to split your code into small chunks which you can then load on demand.
+
+This project setup supports code splitting via [dynamic `import()`](http://2ality.com/2017/01/import-operator.html#loading-code-on-demand). Its [proposal](https://github.com/tc39/proposal-dynamic-import) is in stage 3. The `import()` function-like form takes the module name as an argument and returns a [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) which always resolves to the namespace object of the module.
+
+Here is an example:
+
+### `moduleA.js`
+
+```js
+const moduleA = 'Hello';
+
+export { moduleA };
+```
+
+### `App.js`
+
+```js
+import React, { Component } from 'react';
+
+class App extends Component {
+  handleClick = () => {
+    import('./moduleA')
+      .then(({ moduleA }) => {
+        // Use moduleA
+      })
+      .catch(err => {
+        // Handle failure
+      });
+  };
+
+  render() {
+    return (
+      <div>
+        <button onClick={this.handleClick}>Load</button>
+      </div>
+    );
+  }
+}
+
+export default App;
+```
+
+This will make `moduleA.js` and all its unique dependencies as a separate chunk that only loads after the user clicks the 'Load' button.
+
+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).
+
+Also check out the [Code Splitting](https://reactjs.org/docs/code-splitting.html) section in React documentation.