Add OpenSSF Best Practices badge to README
MODIFY
README.md
README.md
<a href="https://github.com/urllib3/urllib3/actions?query=workflow%3ACI"><img alt="Coverage Status" src="https://img.shields.io/badge/coverage-100%25-success" /></a>
<a href="https://github.com/urllib3/urllib3/actions?query=workflow%3ACI"><img alt="Build Status on GitHub" src="https://github.com/urllib3/urllib3/workflows/CI/badge.svg" /></a>
<a href="https://urllib3.readthedocs.io"><img alt="Documentation Status" src="https://readthedocs.org/projects/urllib3/badge/?version=latest" /></a>
+ <a href="https://bestpractices.coreinfrastructure.org/projects/6227"><img alt="CII Best Practices" src="https://bestpractices.coreinfrastructure.org/projects/6227/badge" /></a>
</p>
urllib3 is a powerful, *user-friendly* HTTP client for Python. Much of the

Add OpenSSF Best Practices badge to README