Adding a custom property to scope is not documented

At the bottom of the documentation it says that you can add your own scope properties in addition to message and title, however there's a lot of documentation missing on that functionality.

There is no documentation that specifies that you must create your own scope, add your custom property to it and then set the undocumented scope property in the notification:

```
var scope = $rootScope.$new(false);
scope.event = notificationEvent;
//show toast
Notification({
title: notificationEvent.displayText,
scope: scope,
templateUrl: '/client/app/core/ui/directives/events/signalrEventItem.html'
});
```

Would you accept a pull request for this?