README update with relationship to current Rust?

[cameronelliott]

Thank you for creating coroutine-rs

I'm just learning, but it seems Rust has some form of either:
coroutines, semiroutines or generators, as was implemented to build async/await into Rust.

Generators Pull Request
Claim futures/await is build upon generators/coroutines

It would be really lovely if the README had some explanatory text discussing the currently use cases for this package.
Where it shines, where it might make sense to use Rust core features.

It's really very hard to figure out the should I use features from this Crate, or build in Rust features as a newcomer to the Rust world.

[zonyitoo]

This crate was created before Rust's builtin async/await feature was announced. It would be a lot nicer to use the builtin async/await.