add Enterprise only note for follow events

Author: tcaldwell-x

x-api/activity/introduction.mdx

@@ -51,6 +51,10 @@ Follow events are triggered when a user follows or unfollows another user.
 | `follow.follow` | Fired when a user follows another user | `user_id` |
 | `follow.unfollow` | Fired when a user unfollows another user | `user_id` |
 
+<Note>
+**Enterprise Only:** The `follow.follow` and `follow.unfollow` events are only available to Enterprise and Partner tier accounts at this time.
+</Note>
+
 ### Spaces Events
 
 Spaces events are triggered when a user starts or ends a Space.