chore: add zh-Hans (Chinese, simplified) translation

[YDX-2147483647]

Blocked by #20.

Preview: https://ydx-2147483647.github.io/typst/.

Feedbacks from the Chinese community

• Font: HK Grotesk and BIZ UDGothic are not suitable for Chinese. Although we can recognize they're Han characters, it feels strange.
• Discord icon: Discord is not popular in China (at least in mainland). We use QQ. Simple Icons has (a CC0 variant of) its icon.

Other known issues that need to be fixed outside typst-docs-web

The following issues are out of the scope of typst-docs-web.

• **译者注：** collides with 💡.
• /reference/math/attach should be put at /reference/math/attach/, to be consistent with other pages.

[3w36zj6]

Would zh-cmn-Hans-CN be better than zh-Hans?

Feedback from the Chinese community is informative. Since the appropriate font family may differ between languages, it would be good to either make fonts easily replaceable or switch to a font that can be used consistently across many languages. Also, I think it would be convenient to make it easy to extend the social icons in the header.

[YDX-2147483647]

Would zh-cmn-Hans-CN be better than zh-Hans?

Yes, that's the most accurate code. However, I don't want it to be too specific. Considering that only one single Chinese translation is provided at present, I think zh-Hans is better.

In fact, I've considered between zh-Hans and zh-CN. I chose zh-Hans because CLReq uses that.

Also, I think it would be convenient to make it easy to extend the social icons in the header.

How about changing discordServerUrl: string; githubRepositoryUrl: string to social: OrderedMap<'github' | 'discord' | 'qq' | 'homepage' | …, { url: string, icon: Fragment, aria_text: string }>?
This can also support reordering the icons in the Header and Footer.

either make fonts easily replaceable or switch to a font that can be used consistently across many languages

I inspect the current design and have no idea how can the former be implemented…
As for the latter, I guess Source Han Sans & Serif are the only options?