Update README.md (#65)

Author: koxudaxi

README.md

@@ -5,6 +5,7 @@
 [![PyPI - Python Version](https://img.shields.io/pypi/pyversions/pydataapi)](https://pypi.python.org/pypi/pydataapi)
 [![codecov](https://codecov.io/gh/koxudaxi/py-data-api/branch/master/graph/badge.svg)](https://codecov.io/gh/koxudaxi/py-data-api)
 ![license](https://img.shields.io/github/license/koxudaxi/py-data-api.svg)
+[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
 
 py-data-api is a user-friendly client which supports SQLAlchemy models.
 Also, the package includes DB API 2.0 Client and SQLAlchemy Dialects.