docs: Update represented-file fiddle tutorial (#29245)

* Update represented-file fiddle.

* add index and code back to guide

Co-authored-by: Ethan Arrowood <ethan.arrowood@gmail.com>

docs/fiddles/features/represented-file/main.js

@@ -4,10 +4,7 @@ const os = require('os');
 function createWindow () {
   const win = new BrowserWindow({
     width: 800,
-    height: 600,
-    webPreferences: {
-      nodeIntegration: true
-    }
+    height: 600
   })
 
   win.loadFile('index.html')