Add badges

Author: harupy

README.md

@@ -3,6 +3,8 @@
 [![pypi badge](https://img.shields.io/pypi/v/sphinx-plotly-directive?color=blue)](https://pypi.org/project/sphinx-plotly-directive/)
 ![CI](https://github.com/harupy/sphinx-plotly-directive/workflows/CI/badge.svg)
 [![Documentation Status](https://readthedocs.org/projects/sphinx-plotly-directive/badge/?version=latest)](https://sphinx-plotly-directive.readthedocs.io/en/latest/?badge=latest)
+[![Imports: isort](https://img.shields.io/badge/%20imports-isort-%231674b1?style=flat&labelColor=ef8336)](https://pycqa.github.io/isort/)
+[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
 
 A directive for including a Plotly figure in a Sphinx document.