Implement link in left hand navigation panel to top of page. Maybe?

@Bezart 已经在做这个了。

开始于 2022年8月27日。

I was reading [script-async-defer](https://javascript.info/script-async-defer), and I started to navigate backwards up the page using the navigation panel on the left. I have used the navigation panel before to go down the page, but I prefer to use the mouse wheel and keep my pointer in the middle of the screen.

However, this time I decided to scan the article in reverse and I noticed that it was useful for reinforcing what I had just read. However, I could not get back to the very top.

I notice that the only place that `href="#"` is used in the source code is in the code examples.

Maybe, a link at the top of the navigation panel to the top of the page would be useful. For example:
`Scripts: async, defer`

And maybe another one at the bottom of the content:
`Back to top of page`

I can find a use case for both buttons.
* The link in the navigation panel would be used as described above.
* I would use the `Back to top of page` link in this way, for example:
1. I would scan the page relatively quickly using my mouse wheel, until I reached the bottom of the page.
2. At the bottom, I would press `Back to top of page` and then read the whole page again more slowly.