Add Docker badge

[ci skip]

README.md

@@ -1,6 +1,7 @@
 # docker-node-sass
 
 [![Build Status](https://drone.autonomic.zone/api/badges/3wordchant/docker-node-sass/status.svg)](https://drone.autonomic.zone/3wordchant/docker-node-sass)
+[![](https://img.shields.io/docker/v/3wordchant/node-sass)](https://hub.docker.com/r/3wordchant/node-sass/)
 
 Docker image for node-sass, based on this blog post:
 http://johnbokma.com/blog/2021/06/17/a-docker-image-for-sass.html