add album api & unit test, improve document

router/album.js

@@ -0,0 +1,18 @@
+const express = require("express")
+const router = express()
+const { createRequest } = require("../util/util")
+
+router.get("/", (req, res) => {
+  const id = req.query.id
+  createRequest(`/api/album/${id}`, 'GET', null)
+    .then(result => {
+      res.setHeader("Content-Type", "application/json")
+      res.send(result)
+    })
+    .catch(err => {
+      res.status(502).send('fetch error')
+    })
+})
+
+
+module.exports = router