Add zenoh to the list of async-std ecosystem

[kydos]

zenoh is an innovative communication framework entirely written in async Rust. We focus on performance, safety and usability. We think that zenoh fills an important gap in the async Rust ecosystem and as such would like to be added to the list.

I will submit a pull request with the suggested changed to the readme.

[kydos]

Hello, this pull request has been here for two years. We have been extremely committed to async-std, and have published several benchmarks that show how async-std over performs Tokio. Additionally, Zenoh (https://zenoh.io) which is 100% Rust-based and once again based on async-std, is used in several high visibility projects, including the Indy Autonomous Channel.

Looking forward to hear your thoughts.