Update README.md

Author: PierrickVoulet

solutions/ooo-assistant/README.md

@@ -1,7 +1,7 @@
 # Build a Google Workspace add-on extending all UIs
 
-**Warning:** This sample builds a Chat app as a Google Workspace add-on. It's only available in the [Developer Preview Program](https://developers.google.com/workspace/preview).
-
 The add-on extends the following Google Workspace UIs: Chat, Calendar, Gmail, Drive, Docs, Sheets, and Slides.
 
 It relies on app commands in Chat, and homepage and universal actions in the others.
+
+It's featured in [this YT video](https://www.youtube.com/watch?v=pDthZ2xssDc).