Merge pull request #960 from brainwane/pypi-badge

Add PyPI badge

Author: JustinCappos

README.md

@@ -6,6 +6,7 @@
 [![Python 3](https://pyup.io/repos/github/theupdateframework/tuf/python-3-shield.svg)](https://pyup.io/repos/github/theupdateframework/tuf/)
 [![FOSSA Status](https://app.fossa.com/api/projects/custom%2B162%2Fgithub.com%2Ftheupdateframework%2Ftuf.svg?type=shield)](https://app.fossa.com/projects/custom%2B162%2Fgithub.com%2Ftheupdateframework%2Ftuf?ref=badge_shield)
 [![CII](https://bestpractices.coreinfrastructure.org/projects/1351/badge)](https://bestpractices.coreinfrastructure.org/projects/1351)
+[![PyPI](https://img.shields.io/pypi/v/tuf)](https://pypi.org/project/tuf/)
 
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 This repository is the **reference implementation** of