[documentation] Better document webshot / webshot2 usage

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Would you mind document better the usage / availability of webshot / webshot2? Actually I get to know that I can use webshot2 only after reading GH discussions on already closed issue, namely https://github.com/yihui/knitr/issues/2276#issuecomment-1686948876. (as a side note - only using webshot2 I could solve the issue). When I googled this topic for the very first time I end up on an article in your bookdown book which also does not mention webshot2. For people with the same issue as mine, it would be great to have it listed somewhere in the Chunks Option article or anywhere in the docs.

yihui / knitr

[documentation] Better document webshot / webshot2 usage #2315