Fix for ReactDOM.createRoot() example (#5437)

* Fix for ReactDOM.createRoot() example

* Update createRoot.md

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

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

@@ -23,6 +23,8 @@ const root = createRoot(domNode, options?)
 Call `createRoot` to create a React root for displaying content inside a browser DOM element.
 
 ```js
+import { createRoot } from 'react-dom/client';
+
 const domNode = document.getElementById('root');
 const root = createRoot(domNode);
 ```