Update onAuthorizer custom callback error

Author: fbenevides

README.md

@@ -290,7 +290,7 @@ Called when a member is removed from the presence channel.
 
 #### `onAuthorizer`
 
-> :warning: Currently on web release/profile mode this doesn't work, we're still investigating this.
+> :warning: Currently this feature is not working on iOS. We're working to get this done asap.
 
 When passing the `onAuthorizer()` callback to the `init()` method, this callback is called to request auth information. Learn how
 to [generate the correct auth signatures](https://pusher.com/docs/channels/library_auth_reference/auth-signatures/)