Documentation: Add FAQ about Nextjs plugin in portable stories

docs/_snippets/vite-includeStorybookNextjsPlugin.md

@@ -0,0 +1,9 @@
+```ts filename="vitest.config.ts" renderer="react" language="ts"
+import { defineConfig } from "vite";
+import { storybookNextJsPlugin } from '@storybook/nextjs-vite/vite-plugin'
+
+export default defineConfig({
+  // only necessary when not using @storybook/addon-vitest, otherwise the plugin is loaded automatically
+  plugins: [storybookNextJsPlugin()],
+});
+```

docs/writing-tests/integrations/stories-in-unit-tests.mdx

@@ -79,6 +79,16 @@ Storybook provides community-led addons for other frameworks like [Vue 2](https:
   <CodeSnippets path="reuse-args-test.md" />
 
   {/* prettier-ignore-end */}
+
+  ### Next.js Vite cannot find the module
+
+  If you are seeing error messages like `Cannot find module 'sb-original/image-context'` ensure you have included `storybookNextJsPlugin`.
+
+  {/* prettier-ignore-start */}
+
+  <CodeSnippets path="vite-includeStorybookNextjsPlugin.md" />
+
+  {/* prettier-ignore-end */}
 </IfRenderer>
 
 <IfRenderer renderer="vue">