Doc async runtime support

Cargo.toml

@@ -20,6 +20,9 @@ tls = ["rustls", "rustls-pemfile", "webpki-roots"]
 sasl = ["sasl-gssapi", "sasl-digest-md5"]
 sasl-digest-md5 = ["rsasl/unstable_custom_mechanism", "md5", "linkme", "hex"]
 sasl-gssapi = ["rsasl/gssapi"]
+tokio = ["asyncs/tokio"]
+smol = ["asyncs/smol"]
+async-global-executor = ["asyncs/async-global-executor"]
 
 [dependencies]
 bytes = "1.1.0"

src/lib.rs

@@ -18,6 +18,14 @@
 //! * `sasl`: Toggle SASL support.
 //! * `sasl-gssapi`: Toggle only GSSAPI SASL support. This relies on binding package `libgssapi-sys`.
 //! * `sasl-digest-md5`: Toggle only DIGEST-MD5 SASL support.
+//!
+//! ## Async runtime support
+//! This library uses [asyncs](https://docs.rs/asyncs) and [spawns](https://docs.rs/spawns) to
+//! spawn asynchronous tasks. It exposes runtime feature flags for handy. Please refer their docs
+//! for references.
+//! * `tokio`: Toggle support for [tokio](https://docs.rs/tokio).
+//! * `smol`: Toggle support for [smol](https://docs.rs/smol) builtin global executor.
+//! * `async-global-executor`: Toggle support for [async-global-executor](https://docs.rs/async-global-executor).
 
 mod acl;
 mod chroot;