docs: add OSSF donation announcement

Signed-off-by: Ulises Gascón <ulisesgascongonzalez@gmail.com>

README.md

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 **Simplify OpenSSF Scorecard tracking in your organization with automated markdown and JSON reports, plus optional GitHub issue alerts.**
 
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+**📢 IMPORTANT**
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+This project is now part of the [OpenSSF](https://openssf.org/) organization. You can find more information about it in [this announcement](https://github.com/ossf/scorecard-monitor/issues/79).
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 ## 🔮 About
 
 If you're feeling overwhelmed by an avalanche of repository scorecards in your organization, you can breathe easy: Automation is here to make your life easier! It will streamline the process of keeping track of them all by providing a comprehensive report in Markdown and a local database in JSON with all the scores. Furthermore, to stay on top of any changes in the scores, you can choose to get notifications through Github Issues.