docs(staletime): add clarification around prefetch false (#65252)
## Why?
Add clarification around when the `prefetch` prop on the `Link`
component is set to `false`.
- x-ref:
https://github.com/vercel/next.js/issues/51788#issuecomment-2088521708
-
https://github.com/vercel/next.js/blob/canary/test/e2e/app-dir/app-client-cache/client-cache.test.ts#L202
Closes NEXT-3275