Update README to include performance note

README.md

@@ -28,3 +28,16 @@ can use it with non-blocking/asynchronous `TcpStream`s from and couple it togeth
 ## Features
 
 As with [`tungstenite-rs`](https://github.com/snapview/tungstenite-rs) TLS is supported on all platforms using [`native-tls`](https://github.com/sfackler/rust-native-tls) or [`rustls`](https://github.com/ctz/rustls) through feature flags: `native-tls`, `rustls-tls-native-roots` or `rustls-tls-webpki-roots` feature flags. Neither is enabled by default. See the `Cargo.toml` for more information. If you require support for secure WebSockets (`wss://`) enable one of them.
+
+## Is it performant?
+
+In essence, `tokio-tungstenite` is a wrapper for `tungstenite`, so the performance is capped by the performance of `tungstenite`. `tungstenite`
+has a decent performance, but it's definitely not the fastest WebSocket library in the world at the moment of writing this note.
+
+In majority of the cases the provided performance is more than enough (both `tungstenite` and `tokio-tungstenite` have been used in production
+scenarios for web real-time communication), however if performance is of a paramount importance for you (especially if you send **large messages**),
+then you might want to check other libraries that are performance focused or you could file a PR against `tungstenite` to improve the performance!
+
+We are aware of changes that both `tungstenite` and `tokio-tungstenite` need in order to fill that gap of ~30% performance difference between `tungstenite`
+and more performant libraries like `fastbwebsockets`, but we have not worked on that yet as it was not required for the original use case for which `tungstenite`
+was designed. That being said, performance improvements are welcome. For a quick summary of the performance problems, see [this comment](https://github.com/snapview/tungstenite-rs/issues/352).