Documentation: Update Next.js portable stories instructions for Vitest

docs/_snippets/portable-stories-vitest-compose-stories.md

@@ -1,6 +1,7 @@
 ```tsx filename="Button.test.tsx" renderer="react" language="ts"
 import { test, expect } from 'vitest';
 import { screen } from '@testing-library/react';
+// 👉 Using Next.js? Import from @storybook/nextjs instead
 import { composeStories } from '@storybook/react';
 
 // Import all stories and the component annotations from the stories file

docs/api/portable-stories/portable-stories-vitest.mdx

@@ -28,7 +28,7 @@ sidebar:
 
   <If renderer="react">
     <Callout variant="warning">
-      **Using `Next.js`?** Next.js requires specific configuration that is only available in [Jest](./portable-stories-jest.mdx). The portable stories API is not supported in Next.js with Vitest.
+      **Using `Next.js`?** You can test your Next.js stories with Vitest by installing and setting up the [`vite-plugin-storybook-nextjs`](https://github.com/storybookjs/vite-plugin-storybook-nextjs) package. 
     </Callout>
   </If>