Add beta tag to docs!

Created by: Joelkw

@felixfbecker if you want to get fancy and it'd take you less than 5 minutes, it would be cool to add the beta tag from the product to the docs as well (screenshot) (both light/dark versions since docs can be light/dark). Otherwise, making a fast lightweight change and will merge.

(Also @felixfbecker, please see the note here about (not) having code insights in the sidebar if you haven't yet – this is an intentional omission.)