Add the tokio02 feature flag

Cargo.toml

@@ -51,6 +51,7 @@ alloc = [
   "futures-core/alloc",
   "pin-project-lite",
 ]
+tokio02 = ["smol/tokio02"]
 
 [dependencies]
 async-attributes = { version = "1.1.1", optional = true }

src/lib.rs

@@ -214,6 +214,15 @@
 //! features = ["attributes"]
 //! ```
 //!
+//! Compatibility with the `tokio` runtime is possible using the `tokio02`
+//! Cargo feature:
+//!
+//! ```toml
+//! [dependencies.async-std]
+//! version = "1.6.0"
+//! features = ["tokio02"]
+//! ```
+//!
 //! Additionally it's possible to only use the core traits and combinators by
 //! only enabling the `std` Cargo feature:
 //!