[Docs] Update po/README.md with Correct Translator Web Interface URL

[ManuelFCastillo]

Current State

The README.md file references the outdated web interface URL for translators. It currently points to:
http://translate.sugarlabs.org/projects/MusicBlocks/

Desired State

Update the README.md file to reflect the new web interface URL for translators:
https://weblate.sugarlabs.org

---

Checklist

• I have read and followed the project's code of conduct.
• I have searched for similar issues before creating this one.
• I have provided all the necessary information to understand and reproduce the issue.
• I am willing to contribute to the resolution of this issue.

---

Thank you for contributing to our project! We appreciate your help in improving it.

📚 See contributing instructions.

🙋🏾🙋🏼 Questions: Community Matrix Server.