README: add pre-commit badge

README.md

@@ -2,6 +2,7 @@
 
 [![Build Status](https://github.com/kamailio/kamailio/actions/workflows/main.yml/badge.svg)](https://github.com/kamailio/kamailio/actions)
 [![Code Triage Badge](https://www.codetriage.com/kamailio/kamailio/badges/users.svg)](https://www.codetriage.com/kamailio/kamailio)
+[![pre-commit](https://img.shields.io/badge/pre--commit-enabled-brightgreen?logo=pre-commit)](https://github.com/pre-commit/pre-commit)
 
 Project Website: