2.x: update readme parallel example (#5062)
2.x: update readme parallel example (#5062)


ReactiveX/RxJava,akarnokd/RxJava,ReactiveX/RxJava,artem-zinnatullin/RxJava,NiteshKant/RxJava,AttwellBrian/RxJava,AttwellBrian/RxJava,reactivex/rxjava,reactivex/rxjava,artem-zinnatullin/RxJava,akarnokd/RxJava,NiteshKant/RxJava