make host and port configurable through HOST and PORT

src/main.rs

···
 
 #[actix_web::main]
 async fn main() -> std::io::Result<()> {
+    let host = std::env::var("HOST").unwrap_or(String::from("127.0.0.1"));
+    let port = std::env::var("PORT")
+        .map(|x| x.parse::<u16>().unwrap_or(60000))
+        .unwrap_or(60000);
+
+    println!(
+        "Starting http server on POST http://{}:{}/notify",
+        host, port
+    );
+
     HttpServer::new(|| App::new().service(notify))
-        .bind(("127.0.0.1", 3000))?
+        .bind((host, port))?
         .run()
         .await
 }