adds badge to README

Author: kyleniemeyer

README.md

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+![CI badge](https://github.com/SoftwareDevEngResearch/packaging-examples/actions/workflows/test.yml/badge.svg)
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 # Packaging examples
 
 Borrowed from [Matthew Feickert](https://github.com/matthewfeickert-talks/talk-urssi-summer-school-2024), and example code from [SciPy documentation](https://docs.scipy.org/doc/scipy-1.11.2/tutorial/optimize.html).