Add OpenSSF Best Practices badge to README
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+ <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
