Fix documentation link

[scpeters]

🦟 Bug fix

Fixes broken link in readme

Summary

The documentation page linked in the README was renamed in https://github.com/maliput/maliput_documentation/pull/99, so update the link accordingly.

Checklist

• [X] Signed all commits for DCO
• [ ] Added tests
• [X] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] Consider updating Python bindings (if it affects the public API)

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.