Add note about open-sesame

Author: jamesdaniels

README.md

@@ -29,6 +29,14 @@
 
 This repository is maintained by Googlers but is not a supported Firebase product. Issues here are answered by maintainers and other community members on GitHub on a best-effort basis.
 
+# Enable framework-awareness
+
+This is an experimental addon to the Firebase CLI to add web framework support, to enable it call the following:
+
+```shell
+firebase --open-sesame frameworkawareness
+```
+
 # Deploy Next.js
 
 Easily deploy your Next.js application to Firebase and serve dynamic content to your users.