docs: add CI badge to README

Author: ancongui

README.md

@@ -1,5 +1,7 @@
 # Firefly Event Driven Architecture Library
 
+[![CI](https://github.com/fireflyframework/fireflyframework-eda/actions/workflows/ci.yml/badge.svg)](https://github.com/fireflyframework/fireflyframework-eda/actions/workflows/ci.yml)
+
 [![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://opensource.org/licenses/Apache-2.0)
 [![Java Version](https://img.shields.io/badge/Java-21+-orange.svg)](https://openjdk.java.net/)
 [![Spring Boot](https://img.shields.io/badge/Spring%20Boot-3.2+-green.svg)](https://spring.io/projects/spring-boot)