add dockerfile to serve content on port 3000

add a println! statement to check that the service starts serving

src/main.rs

@@ -21,6 +21,8 @@ async fn main() {
         .route("/api/update.php", post(the_doors));
 
     let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
+
+    println!("Start serving");
     axum::serve(listener, app).await.unwrap();
 }