add more askai help in blog post

Author: slorber

website/blog/releases/3.9/index.mdx

@@ -43,12 +43,14 @@ In [#11327](https://github.com/facebook/docusaurus/pull/11327) and [#11421](http
 </BrowserWindow>
 ```
 
-:::tip DocSearch v4 is optional
+:::tip DocSearch v4 is opt-in
 
 Docusaurus v3 adds support for DocSearch v4 while keeping support for DocSearch v3.
 
 Existing sites using DocSearch v3 can either stay on v3 or upgrade to v4 using their package manager (npm command: `npm update @docsearch/react`).
 
+When using DocSearch v4, the new AskAI feature is not enabled by default: you also need to [create an AskAI assistant](https://docsearch.algolia.com/docs/v4/askai/) and add it to the [`themeConfig.algolia.askAi` config attribute](/docs/search#ask-ai).
+
 :::
 
 ## i18n improvements