Improve json documentation (#245)

Co-authored-by: Rob Ede <robjtede@icloud.com>

examples/responses/src/json_resp.rs

@@ -1,17 +1,18 @@
 // <json-resp>
-use actix_web::{get, web, HttpResponse, Result};
-use serde::{Deserialize, Serialize};
+use actix_web::{get, web, Responder, Result};
+use serde::Serialize;
 
-#[derive(Serialize, Deserialize)]
+#[derive(Serialize)]
 struct MyObj {
     name: String,
 }
 
 #[get("/a/{name}")]
-async fn index(obj: web::Path<MyObj>) -> Result<HttpResponse> {
-    Ok(HttpResponse::Ok().json(MyObj {
-        name: obj.name.to_string(),
-    }))
+async fn index(name: web::Path<String>) -> Result<impl Responder> {
+    let obj = MyObj {
+        name: name.to_string(),
+    };
+    Ok(web::Json(obj))
 }
 
 #[actix_web::main]