Rename CII to OpenSSF in badge alt text

[hugovk]

https://bestpractices.coreinfrastructure.org/en says:

This project was formerly known as the Core Infrastructure Initiative (CII) Best Practices badge. and was originally developed under the CII. It is now part of the OpenSSF Best Practices Working Group (WG). The OpenSSF is a foundation of the Linux Foundation (LF). The project was formally renamed from "CII Best Practices badge" on 2021-12-24.

However, the badge templates still have the CII name.

For example at https://bestpractices.coreinfrastructure.org/en/projects/6331 :

You can show your badge status by embedding this in your markdown file:
[![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/6331/badge)](https://bestpractices.coreinfrastructure.org/projects/6331)
or by embedding this in your HTML:
<a href="https://bestpractices.coreinfrastructure.org/projects/6331"><img src="https://bestpractices.coreinfrastructure.org/projects/6331/badge"></a>

This PR renames CII to OpenSSF in the Markdown badge alt text.

(The HTML badge doesn't have alt text, but should do.)

[david-a-wheeler]

Thank you so much! You're absolutely right. I'll merge this once we've gotten some other things through the pipeline.