Fixed code example in README

A call to the `format!` macro was implying the use of a named argument
called `name` in the format string, but the argument wasn't specified. I fixed
this by using the simple {} notation in the format string and passing
the `name` variable as a second argument.

actix-web/README.md

@@ -58,7 +58,7 @@ use actix_web::{get, web, App, HttpServer, Responder};
 
 #[get("/hello/{name}")]
 async fn greet(name: web::Path<String>) -> impl Responder {
-    format!("Hello {name}!")
+    format!("Hello {}!", name)
 }
 
 #[actix_web::main] // or #[tokio::main]