Update project-structure.md (#3166)

Small path update

docs/pages/guides/project-structure.md

@@ -41,7 +41,7 @@ That's it. But now everywhere else in my application instead of requiring `pg` d
 ```js
 // notice here I'm requiring my database adapter file
 // and not requiring node-postgres directly
-import * as db from '../db.js'
+import * as db from '../db/index.js'
 
 app.get('/:id', async (req, res, next) => {
   const result = await db.query('SELECT * FROM users WHERE id = $1', [req.params.id])