add pre-commit and black to readme

README.md

@@ -1,6 +1,6 @@
 # Minimalistic Gridworld Environment (MiniGrid)
 
-[![Build Status](https://travis-ci.org/maximecb/gym-minigrid.svg?branch=master)](https://travis-ci.org/maximecb/gym-minigrid)
+[![pre-commit](https://img.shields.io/badge/pre--commit-enabled-brightgreen?logo=pre-commit&logoColor=white)](https://pre-commit.com/) [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
 
 There are other gridworld Gym environments out there, but this one is
 designed to be particularly simple, lightweight and fast. The code has very few