Add Deno example

[ElianCodes]

Changes

• Adds a Deno example based on the basics example.
• Changes the preview command to deno run --allow-net --allow-read ./dist/server/entry.mjs
• No changeset required

Testing

Tested locally, explained in https://www.elian.codes/blog/22-05-06-deploying-astro-on-deno/

Docs

The only change we might need to add to this example, is explain why the npm run preview command has changed to the native Deno CLI

[changeset-bot]

⚠️ No Changeset found

Latest commit: 4f0cd3d

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[Jutanium]

From the docs perspective: I'm preparing an explanation for astro preview and why it doesn't work for server builds. This PR provides a great example for what a preview command should look like for SSR!

[ElianCodes]

@Jutanium, If you need me to help anywhere on the docs, lemme know!

[sarah11918]

Docs is cool with README as long as one comment is addressed!