add axum && example server

src/main.rs

@@ -1,3 +1,13 @@
-fn main() {
-    println!("Hello, world!");
+use axum::{routing::get, Router};
+
+#[tokio::main]
+async fn main() {
+    // build our application with a single route
+    let app = Router::new().route("/", get(|| async { "Hello, World!" }));
+
+    // run it with hyper on localhost:3000
+    axum::Server::bind(&"0.0.0.0:3000".parse().unwrap())
+        .serve(app.into_make_service())
+        .await
+        .unwrap();
 }