Update createRoot.md

- remove indent spaces
- fix codeblock fences

Author: NivaldoFarias

src/content/reference/react-dom/client/createRoot.md

@@ -549,7 +549,9 @@ const root = createRoot(container, {
   }
 });
 root.render(<App />);
-``````js src/App.js
+```
+
+```js src/App.js
 import { useState } from 'react';
 
 export default function App() {