docs(lib): document backport and deprecated features (#3166)

Author: seanmonstar

README.md

@@ -24,7 +24,7 @@ libraries and applications.
 
 If you are looking for a convenient HTTP client, then you may wish to consider
 [reqwest](https://github.com/seanmonstar/reqwest). If you are looking for a
-convenient HTTP server, then you may wish to consider [warp](https://github.com/seanmonstar/warp).
+convenient HTTP server, then you may wish to consider [Axum](https://github.com/tokio-rs/tokio).
 Both are built on top of this library.
 
 ## Contributing

src/lib.rs

@@ -53,6 +53,8 @@
 //!   connectors and acceptors for TCP, and a default executor.
 //! - `tcp`: Enables convenient implementations over TCP (using tokio).
 //! - `stream`: Provides `futures::Stream` capabilities.
+//! - `backports`: 1.0 functionality backported to 0.14.
+//! - `deprecated`: opt-in to deprecation warnings to prepare you for 1.0.
 //!
 //! [feature flags]: https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section