chore(docs): add missing import to react index.mdx

Author: 1brahimmohamed

docs/react/index.mdx

@@ -21,7 +21,7 @@ and [configure TanStack Query](https://tanstack.com/query/latest/docs/framework/
 
 ```jsx
 import { initializeApp } from 'firebase/app';
-import { QueryClientProvider } from '@tanstack/react-query';
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 
 // TODO: Replace the following with your app's Firebase project configuration
 const firebaseConfig = {
@@ -89,4 +89,4 @@ function MyApplication() {
 }
 ```
 
-TanStack Query Firebase provides hooks for all Firebase services, supporting both mutations and queries.
+TanStack Query Firebase provides hooks for all Firebase services, supporting both mutations and queries.