docs: clarify what you can build with SvelteKit

[benmccann]

I've seen a really depressing number of people saying you can't build a SPA with SvelteKit. Some portion of that may be due to sveltejs/kit#12580, which I'm working on, but I also think some of it is just ignorance or confusion. I'm hoping this change will help on the education side

[changeset-bot]

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Latest commit: a1eb1e4

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-15461-svelte.vercel.app/

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@15461

[benmccann]

The deploy is failing, but is sure looks like its caching an old version and I'm not sure how to address that as I've tried redeploying already. I would say we should just merge this if we're happy with the text and if it's still an issue in the sveltejs/svelte.dev PR then I can look at it some more then