feat: add the example to the app

back-end/src/app.ts

@@ -1,9 +1,12 @@
 import express from 'express';
-const app = express();
-const port = 3000;
+import db from './db';
 
-app.get('/', (req, res) => {
-    res.send('Hello World!');
+const app = express();
+const port = process.env.PORT ?? 3000;
+
+app.get('/', async (_req, res) => {
+  const message = await db.example_request();
+  res.send(message);
 });
 
 app.listen(port, () => {