Update docs: Next.js turbopack support

[onmax]

Blocked By

onmax/nimiq-starter#5

What

Starter repo splitting Next.js into webpack vs turbopack variants. Docs need update for turbopack-specific setup.

Action Needed

Once onmax/nimiq-starter#5 is resolved:

• Document turbopack starter option
• Add any turbopack-specific Nimiq integration notes if needed
• Update links/examples if referencing Next.js starter