add pypi badge

Author: HugoMVale

README.md

@@ -3,6 +3,7 @@
 [![Test-Linux](https://github.com/HugoMVale/odrpack-python/actions/workflows/test-linux.yml/badge.svg)](https://github.com/HugoMVale/odrpack-python/actions)
 [![codecov](https://codecov.io/gh/HugoMVale/odrpack-python/graph/badge.svg?token=B9sFyJiweC)](https://codecov.io/gh/HugoMVale/odrpack-python)
 [![Latest Commit](https://img.shields.io/github/last-commit/HugoMVale/odrpack-python)](https://img.shields.io/github/last-commit/HugoMVale/odrpack-python)
+![PyPI - Downloads](https://img.shields.io/pypi/dm/odrpack?label=PyPI%20downloads)
 [![Ask DeepWiki](https://deepwiki.com/badge.svg)](https://deepwiki.com/HugoMVale/odrpack-python)
 
 ## Description