Mention Typst in the PDF guide

[firai]

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Description

I suggest mentioning Typst as an alternative option and linking to the Typst guide in the PDF guide (PDF Basics and/or PDF Engines). While Typst exists as a separate guide, it wasn't immediately obvious that this was a option to generate PDFs when I was looking at the PDF guide. Since Typst is bundled and doesn't require separately installing a TeX distro, trying Typst before TeX may result in quicker time-to-first-PDF, even if Typst isn't as mature.