doc(socketio): improve doc

socketioxide/src/extensions.rs

@@ -6,6 +6,9 @@
 //! to allow concurrent access. Moreover, any value extracted from the map is cloned before being returned.
 //!
 //! This is necessary because [`Extensions`] are shared between all the threads that handle the same socket.
+//!
+//! You can use the [`Extension`](crate::extract::Extension) or
+//! [`MaybeExtension`](crate::extract::MaybeExtension) extractor to extract an extension of the given type.
 
 use std::collections::HashMap;
 use std::fmt;

socketioxide/src/lib.rs

@@ -188,6 +188,7 @@
 //!     Because the socket is not yet connected to the namespace,
 //!     you can't send messages to it from the middleware.
 //! </div>
+//!
 //! See the [`handler::connect`](handler::connect#middleware) module doc for more details on middlewares and examples.
 //!
 //! ## [Emiting data](#emiting-data)