Update the `subscribe` docs
Update the `subscribe` docs

TracyLu/RxScala,joohnnie/RxScala,zjrstar/RxScala,jbripley/RxScala,zhongdj/RxScala,ReactiveX/RxScala,hermanbanken/RxScala,jbripley/RxScala,hermanbanken/RxScala