Add same note as in tutorial to documentation for "Dimension bindings"

[christophsanz]

Since the note from the tutorial is missing from the actual docs, i put the same note into the docs as well.
Original note: https://svelte.dev/tutorial/svelte/dimensions

[pkg-pr-new]

pnpm add https://pkg.pr.new/svelte@14136

commit: 6885596

[changeset-bot]

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Latest commit: 6885596

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[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14136-svelte.vercel.app/

this is an automated message

[Rich-Harris]

thank you!