docs: add minimum sitemap to nuxt.com

[IsraelOrtuno]

❓ Type of change

• [x] 📖 Documentation (updates to the documentation or readme)
• [ ] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [ ] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

I have added a very basic sitemap file for SEO purposes. This could be improved in the future by adding other parameters such as priority and lastmod if there's a way to guess when a content/**/.md file was modified.

Also included the sitemap in the robots.txt as search engines suggest so they can easily find it.

📝 Checklist

• [ ] I have linked an issue or discussion.
• [ ] I have updated the documentation accordingly.

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[atinux]

Thank you so much @IsraelOrtuno ❤️

I think the server code had to move to the nuxt-website-theme repo (we plan to open source in the next weeks), cc @clemcode

[IsraelOrtuno]

Was looking for it for a while to see where it would make more sense but since I did not find it I thought adding it here

[atinux]

It was great to add it here, would be easy for us to move into the theme (beauty of nuxt extends)

[clemcode]

@IsraelOrtuno the code has been moved to the theme repository, and will be up tomorrow. Thanks a lot for the contribution, I will now close the PR.