docs: v3 prepare your site blog post should point users to the upgrad…

…e guide (#10124)

website/blog/2023/09-29-preparing-your-site-for-docusaurus-v3/index.mdx

@@ -7,6 +7,12 @@ slug: /preparing-your-site-for-docusaurus-v3
 image: ./img/social-card.png
 ---
 
+:::warning
+
+This blog post was written when Docusaurus v3 was in beta. There are some changes in dependency versions and upgrade steps you should be aware of if upgrading to Docusaurus v3 current stable releases. Use the [upgrade guide](https://docusaurus.io/docs/next/migration/v3) for the most up-to-date migration steps.
+
+:::
+
 **Docusaurus v3** is now [**in beta**](https://github.com/facebook/docusaurus/discussions/9312) and the official release is around the corner. This is the perfect time to start **preparing your site** for this new major version.
 
 Docusaurus v3 comes with a few **breaking changes**, many of which can be **handled today under Docusaurus v2**. Preparing your site ahead of time can be done incrementally, and will make it easier to upgrade to v3.