add API documentation badge

README.md

@@ -8,6 +8,7 @@
 [![CodeCov](https://codecov.io/gh/aler9/rtsp-simple-server/branch/main/graph/badge.svg)](https://codecov.io/gh/aler9/rtsp-simple-server/branch/main)
 [![Release](https://img.shields.io/github/v/release/aler9/rtsp-simple-server)](https://github.com/aler9/rtsp-simple-server/releases)
 [![Docker Hub](https://img.shields.io/badge/docker-aler9/rtsp--simple--server-blue)](https://hub.docker.com/r/aler9/rtsp-simple-server)
+[![API Documentation](https://img.shields.io/badge/api-documentation-blue)](https://aler9.github.io/rtsp-simple-server)
 
 _rtsp-simple-server_ is a ready-to-use and zero-dependency server and proxy that allows users to publish, read and proxy live video and audio streams through various protocols: