fix tutorial index links

[dckc]

the "your first dapp" link went to contract basics

and it opened in a new window because it was absolute. Links within the docs are relative.

[cloudflare-pages[bot]]

Deploying documentation with    Cloudflare Pages

Latest commit:	86ae1b4
Status:	✅  Deploy successful!
Preview URL:	https://17c53e14.documentation-7tp.pages.dev
Branch Preview URL:	https://dckc-patch-4.documentation-7tp.pages.dev

View logs

[github-actions[bot]]

Cloudflare deployment logs are available here