docs: Add link to v4 docs

Author: amannn

docs/src/pages/blog/next-intl-4-0.mdx

@@ -223,6 +223,8 @@ Afterwards, you can upgrade by running:
 npm install next-intl@v4-beta
 ```
 
+The beta docs are available here: [v4.next-intl.dev](https://v4.next-intl.dev)
+
 I'd love to hear about your experiences with `next-intl@4.0`! Join the conversation in the [discussions](https://github.com/amannn/next-intl/discussions/1631).
 
 ## Thank you!