Resolve "Setup a simple Express project"

Closes #3 (closed)

backend/src/index.ts

+import express from 'express';
+
+const app = express();
+const port = 3000;
+
+app.get('/', (req, res) => {
+  res.send('Hello, World!');
+});
+
+app.listen(port, () => {
+  console.log(`Server started on port ${port}`);
+});