Docs on this method need to be updated. Would be good to add an explanation of what it means to route to particular streams, using possibly "activity" and "messages" as examples.

Also it looks like we've chosen to use `activityStreamId` as the variable naming for the activity streams, so can we rename the parameter naming to:

`options.streams[id].router`

And also add a a parameter line to describe `options.streams[id]`, to indicate it identifies a stream such as "activity" or "notifications"