fix the code block for createRoot typescript error (#4576)

* fix the code block for createRoot typescript error

* added example block code for typescript

* Inline example

Co-authored-by: dan <dan.abramov@gmail.com>

content/blog/2022-03-08-react-18-upgrade-guide.md

@@ -40,9 +40,8 @@ render(<App tab="home" />, container);
 // After
 import { createRoot } from 'react-dom/client';
 const container = document.getElementById('app');
-const root = createRoot(container);
+const root = createRoot(container); // createRoot(container!) if you use TypeScript
 root.render(<App tab="home" />);
-
 ```
 
 We’ve also changed `unmountComponentAtNode` to `root.unmount`: