Depndency on crate "futures" should be mentioned at first use of this crate.

[sateeshkumarb]

In the section Async In Depth the instruction to add crate futures to Cargo.toml appears in the section Updating Mini Tokio. However the example code snippet shown in the earlier section Executors already makes use of functionality from the crate futures. So the dependency on crate futures should be mentioned early itself in the section Executors.