First page of electron docs does not show code for all files in the given example

# Documentation style bug

The first page of the **electron** docs has a section titled **[Running examples with Electron Fiddle​](https://devdocs.io/electron/#running-examples-with-electron-fiddle)**. The documentation on the **[official site](https://www.electronjs.org/docs/latest/#running-examples-with-electron-fiddle)** for the same section has 3 files `main.js`, `preload.js` and `index.html`. However, devdocs shows the code for only `main.js`. There is no way to view the code for the other two files on devdocs.

将 devdocs 页面中的 Electron Fiddle 部分与 Electron 官方网站上的对应部分进行比较。首先跟踪该文档页面的来源和渲染方式；完成标准是示例展示出与官方文档一致的 main.js、preload.js 和 index.html 代码。

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