Update README.md

[Dahka2321]

Update Katana documentation link

Changes:

• Updated outdated Katana documentation link from '/overview.html' to the new correct path
• Removed redundant URL segment to improve link readability
• Ensures documentation reference stays current and accessible

The previous link was broken and led to a 404 error. This update points to the correct documentation location.

[Dahka2321]

@ClementWalter @Eikix please review the documentation link update

[Eikix]

Hi thanks for the PR, for now we're halting PRs and changes to Kakarot RPC. Thanks for understanding