Update README.md

Author: b-yogesh

chartlets.py/README.md

@@ -2,6 +2,7 @@
 
 [![Backend CI workflow](https://github.com/bcdev/chartlets/actions/workflows/backend-ci.yml/badge.svg)](https://github.com/bcdev/chartlets/actions/workflows/backend-ci.yml)
 [![PyPI Version](https://img.shields.io/pypi/v/chartlets)](https://pypi.org/project/chartlets/)
+[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
 
 Chartlets is a software framework that allows websites developed with
 React to be extended by server-side widgets programmed in Python or other