docs: note that the prerenderer can't crawl pages that have SSR disabled

[eltigerchino]

There's some info missing regarding prerendering and ssr needing to both be enabled to have links discoverable by the prerenderer. This causes users some trouble as they need to discover this for themselves. #8688 (comment)

It may have been in our docs at some point but got removed as shown by the documentation link in this older issue that does not work #9913 (comment)

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