docs: add unplugin-auto-export

Please make sure all the requirements are satisfied, otherwise the PR could be closed without further notice.

Checklist

[ ] Title as described.
[ ] Make sure you put things in the right category.
[ ] The description of your item should be a sentence with less than 24 words.
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[ ] Omit unnecessary words already provided in the context (e.g. for Vite, a Vite plugin).
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[ ] The plugin/tool is working with Vite 2.x and onward.
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