docs(readme): update information for Nuxt 4 and pnpm usage

[nicokempe]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Description

This PR updates the README with the following improvements:

• Updated Features section to indicate support for Nuxt 3 and 4.
• Refined wording from "Checkout" -> "Check out" to improve readability and align with standard English usage.
• Updated development instructions to use pnpm instead of yarn/npm, aligning with the current project setup.

These changes ensure the README reflects current compatibility and project conventions.

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes (not applicable for documentation updates)

[netlify]

👷 Deploy request for n3-supabase pending review.

Visit the deploys page to approve it

Name	Link
🔨 Latest commit	6000d72

[vercel]

@nicokempe is attempting to deploy a commit to the NuxtLabs Team on Vercel.

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[pkg-pr-new]

npm i https://pkg.pr.new/@nuxtjs/supabase@519

commit: 6000d72

[larbish]

Readme was getting old! Thanks @nicokempe