doc(streamable): add document for extracting http info (#373)

* docs(streamable): add document for extracting http info

* docs: fix doc test

crates/rmcp/src/transport/streamable_http_server/tower.rs

@@ -44,6 +44,19 @@ impl Default for StreamableHttpServerConfig {
     }
 }
 
+/// # Streamable Http Server
+///
+/// ## Extract information from raw http request
+///
+/// The http service will consume the request body, however the rest part will be remain and injected into [`crate::model::Extensions`],
+/// which you can get from [`crate::service::RequestContext`].
+/// ```rust
+/// use rmcp::handler::server::tool::Extension;
+/// use http::request::Parts;
+/// async fn my_tool(Extension(parts): Extension<Parts>) {
+///     tracing::info!("http parts:{parts:?}")
+/// }
+/// ```
 pub struct StreamableHttpService<S, M = super::session::local::LocalSessionManager> {
     pub config: StreamableHttpServerConfig,
     session_manager: Arc<M>,