docs: add Black badge

README.md

 # Aura Engine
 
-[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](code_of_conduct.md) [![Latest Release](https://gitlab.servus.at/aura/engine/-/badges/release.svg)](https://gitlab.servus.at/aura/engine/-/releases) [![pipeline status](https://gitlab.servus.at/aura/engine/badges/main/pipeline.svg)](https://gitlab.servus.at/aura/engine/-/commits/main) [![coverage report](https://gitlab.servus.at/aura/engine/badges/main/coverage.svg?job=run_test_cases)](https://gitlab.servus.at/aura/engine/-/commits/main) [![security: bandit](https://img.shields.io/badge/security-bandit-yellow.svg)](https://gitlab.servus.at/aura/engine/-/commits/main)
+[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](code_of_conduct.md) [![Latest Release](https://gitlab.servus.at/aura/engine/-/badges/release.svg)](https://gitlab.servus.at/aura/engine/-/releases) [![pipeline status](https://gitlab.servus.at/aura/engine/badges/main/pipeline.svg)](https://gitlab.servus.at/aura/engine/-/commits/main) [![coverage report](https://gitlab.servus.at/aura/engine/badges/main/coverage.svg?job=run_test_cases)](https://gitlab.servus.at/aura/engine/-/commits/main) [![security: bandit](https://img.shields.io/badge/security-bandit-yellow.svg)](https://gitlab.servus.at/aura/engine/-/commits/main) [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
 
 <img src="https://gitlab.servus.at/aura/aura/-/raw/main/assets/images/aura-engine.png" width="120" align="right" />