add PyPI badge (#241)

README.md

@@ -1,8 +1,8 @@
 [![License](https://img.shields.io/badge/License-BSD%203--Clause-blue.svg)](https://opensource.org/licenses/BSD-3-Clause)
+[![PyPI Version](https://img.shields.io/pypi/v/pyro-hydro)](https://pypi.org/project/pyro-hydro)
 [![pylint](https://github.com/python-hydro/pyro2/actions/workflows/pylint.yml/badge.svg)](https://github.com/python-hydro/pyro2/actions/workflows/pylint.yml)
 [![flake8](https://github.com/python-hydro/pyro2/actions/workflows/flake8.yml/badge.svg)](https://github.com/python-hydro/pyro2/actions/workflows/flake8.yml)
 [![pytest-all](https://github.com/python-hydro/pyro2/actions/workflows/pytest.yml/badge.svg)](https://github.com/python-hydro/pyro2/actions/workflows/pytest.yml)
-
 [![github pages](https://github.com/python-hydro/pyro2/actions/workflows/gh-pages.yml/badge.svg)](https://github.com/python-hydro/pyro2/actions/workflows/gh-pages.yml)
 
 [![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/python-hydro/pyro2/main?filepath=examples%2Fexamples.ipynb)