Update documentation URL in setup.py

[anargyri]

Description

Updated the link in setup.py from readthedocs to github.io. This should also update the link on PyPI when there is a new release.

Related Issues

References

Checklist:

• [ ] I have followed the contribution guidelines and code style for this project.
• [ ] I have added tests covering my contributions.
• [ ] I have updated the documentation accordingly.
• [ ] I have signed the commits, e.g. git commit -s -m "your commit message".
• [ ] This PR is being made to staging branch AND NOT TO main branch.