add black badge

README.md

@@ -3,6 +3,7 @@
 [![Pipeline status](https://gitlab.laas.fr/stack-of-tasks/tsid/badges/master/pipeline.svg)](https://gitlab.laas.fr/stack-of-tasks/tsid/commits/master)
 [![Coverage report](https://gitlab.laas.fr/stack-of-tasks/tsid/badges/master/coverage.svg?job=doc-coverage)](http://projects.laas.fr/gepetto/doc/stack-of-tasks/tsid/master/coverage/)
 [![PyPI version](https://badge.fury.io/py/tsid.svg)](https://badge.fury.io/py/tsid)
+[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
 
 TSID is a C++ library for optimization-based inverse-dynamics control based on the rigid multi-body dynamics library [Pinocchio](https://github.com/stack-of-tasks/pinocchio).
 
@@ -114,4 +115,3 @@ If you are (or not) happy with TSID and want to cite it, please use the followin
 	    url = {https://hal.archives-ouvertes.fr/hal-01136936/document},
 	    author = {Andrea Del Prete, Nicolas Mansard, Oscar E Ramos, Olivier Stasse, Francesco Nori}
     }
-