docs: shields.io badges for PyPI version & supported Python versions

README.md

@@ -1,5 +1,7 @@
 # Mitogen
 
+[![PyPI - Version](https://img.shields.io/pypi/v/mitogen)](https://pypi.org/project/mitogen/)
+[![PyPI - Python Version](https://img.shields.io/pypi/pyversions/mitogen)](https://pypi.org/project/mitogen/)
 [![Build Status](https://img.shields.io/github/actions/workflow/status/mitogen-hq/mitogen/tests.yml?branch=master)](https://github.com/mitogen-hq/mitogen/actions?query=branch%3Amaster)
 
 <a href="https://mitogen.networkgenomics.com/">Please see the documentation</a>.