Add build status badge to README

[skip CI]

Author: djmaze

README.md

@@ -1,5 +1,7 @@
 # About this Repo
 
+[![Build Status](https://armdrone.strahlungsfrei.de/api/badges/armhf-docker-library/docker/status.svg)](https://armdrone.strahlungsfrei.de/armhf-docker-library/docker)
+
 This is the Git repo of the Docker [official image](https://docs.docker.com/docker-hub/official_repos/) for [docker](https://registry.hub.docker.com/_/docker/). See [the Docker Hub page](https://registry.hub.docker.com/_/docker/) for the full readme on how to use this Docker image and for information regarding contributing and issues.
 
 The full readme is generated over in [docker-library/docs](https://github.com/docker-library/docs), specificially in [docker-library/docs/docker](https://github.com/docker-library/docs/tree/master/docker).