added API placeholder

api/index.js

@@ -0,0 +1,11 @@
+const express = require('express')
+const app = express()
+const port = 3000
+
+app.get('/', (req, res) => {
+  res.send('Hello World!')
+})
+
+app.listen(port, () => {
+  console.log(`Example app listening on port ${port}`)
+})