Merge pull request #687 from bashtage/black-badge

DOC: Add black badge

Author: bashtage

README.rst

@@ -18,6 +18,10 @@ Up to date remote data access for pandas, works for multiple versions of pandas.
 .. image:: https://readthedocs.org/projects/pandas-datareader/badge/?version=latest
     :target: https://pandas-datareader.readthedocs.io/en/latest/
 
+.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
+     :target: https://github.com/psf/black
+
+
 .. warning::
 
    As of v0.7.0 Google finance and Morningstar have been been immediately deprecated due to