Add CI image status badge

README.md

@@ -1,5 +1,7 @@
 # lila-docker
 
+[![Publish CI image](https://github.com/lichess-org/lila-docker/actions/workflows/ci-image.yml/badge.svg)](https://github.com/lichess-org/lila-docker/actions/workflows/ci-image.yml)
+
 Lichess development environment using Docker Compose, for developing on Mac, Linux, or Windows (via WSL).
 
 The only requirements for running on your local machine are `git` and Docker Desktop. All the other dependencies (Scala, MongoDB, Node.js, etc) are installed and run in Docker containers.