add microbadges

Author: Vladimir Kotal

docker/README.md

@@ -1,3 +1,6 @@
+[![](https://images.microbadger.com/badges/image/opengrok/docker.svg)](https://microbadger.com/images/opengrok/docker "Get your own image badge on microbadger.com")
+[![](https://images.microbadger.com/badges/version/opengrok/docker.svg)](https://microbadger.com/images/opengrok/docker "Get your own version badge on microbadger.com")
+
 # A Docker container for OpenGrok
 
 ## OpenGrok from official source