Updates 'autoreloading' section

examples/autoreload/src/main.rs

@@ -0,0 +1,21 @@
+// <autoreload>
+use actix_web::{web, App, HttpRequest, HttpServer, Responder};
+use listenfd::ListenFd;
+
+fn index(_req: HttpRequest) -> impl Responder {
+    "Hello World!"
+}
+
+fn main() {
+    let mut listenfd = ListenFd::from_env();
+    let mut server = HttpServer::new(|| App::new().route("/", web::get().to(index)));
+
+    server = if let Some(l) = listenfd.take_tcp_listener(0).unwrap() {
+        server.listen(l).unwrap()
+    } else {
+        server.bind("127.0.0.1:3000").unwrap()
+    };
+
+    server.run().unwrap();
+}
+// </autoreload>