Update README for docker images

README

@@ -12,6 +12,8 @@ Download:
 	https://github.com/z3APA3A/3proxy/releases
 	Binaries for devel version (Windows, Linux):
 	https://3proxy.org/download/devel/
+	Docker images:
+	https://hub.docker.com/repository/docker/3proxy/3proxy
 Archive of old versions: https://github.com/z3APA3A/3proxy-archive