[doc] Add github actions CI badge in README

Author: moumoutte

README.md

@@ -3,6 +3,7 @@
 [![pytest](https://img.shields.io/badge/pytest-extension-blue)](https://docs.pytest.org/en/latest/)
 [![Python](https://img.shields.io/pypi/v/pytest-sqlguard)](https://pypi.org/project/pytest-sqlguard/)
 ![GitHub License](https://img.shields.io/github/license/PayLead/pytest-sqlguard)
+![CI](https://github.com/PayLead/pytest-sqlguard/actions/workflows/sqlguard-ci.yml/badge.svg?brand=main)
 
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