You have been added to a User Group
Compatibility: RTM Events API
subteam_self_added event is sent to you when you have been added
to an existing User Group. Clients can use this to update their local
list of User Groups.
This event is not available to bot user subscriptions in the Events API.
Events API compatibility
Subscribe to this event via the Events API.
Events of this type will be wrapped in metadata when sent via the Events API.