added functionality and file structure

src/main.rs

@@ -1,7 +1,13 @@
 #[macro_use] extern crate rocket;
 use rocket::{Rocket, Build};
 
+#[get("/")]
+fn index() -> String {
+    format!("Hello world")
+}
+
 #[launch]
 fn rocket() -> Rocket<Build> {
     rocket::build()
+    .mount("/", routes![index])
 }