docs: Correct create svelte 4 project command

[parml]

People visiting v4.svelte.dev are interested in pre-5 svelte. Latest version of create-svelte package provides no functionality to create a project (it's a notice to use v5). Provided materials created for v4 and earlier need not be simply thrown away, creating a pre-v5 project should still be possible. 6.4.0 seems to be the last version of create-svelte package that can be used to create a v4 svelte project.

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• Prefix your PR title with feat:, fix:, chore:, or docs:.
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.
• If this PR changes code within packages/svelte/src, add a changeset (npx changeset).

Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint

[changeset-bot]

⚠️ No Changeset found

Latest commit: efd1f02

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[Rich-Harris]

thanks!