Updates README with 3.0.0-beta.2 release notes.
Updates README with 3.0.0-beta.2 release notes.

kzaher/RxSwift,ReactiveX/RxSwift,cfraz89/RxSwift,kzaher/RxSwift,ReactiveX/RxSwift,cfraz89/RxSwift,shiratsu/RxSwift,KyoheiG3/RxSwift,kzaher/RxSwift,tottakai/RxSwift,KyoheiG3/RxSwift,cfraz89/RxSwift,shiratsu/RxSwift,cfraz89/RxSwift,ReactiveX/RxSwift,tottakai/RxSwift,kzaher/RxSwift,shiratsu/RxSwift,tottakai/RxSwift,KyoheiG3/RxSwift