README.md: add pre-commit badge

Author: csernazs

README.md

@@ -5,6 +5,7 @@
 [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
 [![Ruff](https://img.shields.io/endpoint?url=https://raw.githubusercontent.com/astral-sh/ruff/main/assets/badge/v2.json)](https://github.com/astral-sh/ruff)
 [![Downloads](https://static.pepy.tech/badge/pytest-httpserver/month)](https://pepy.tech/project/pytest-httpserver)
+[![pre-commit](https://img.shields.io/badge/pre--commit-enabled-brightgreen?logo=pre-commit)](https://github.com/pre-commit/pre-commit)
 
 ## pytest_httpserver