Add drone build

.drone.yml

@@ -0,0 +1,16 @@
+kind: pipeline
+type: docker
+name: dirl
+
+steps:
+- name: publish-container
+  image: plugins/docker
+  settings:
+    username:
+      from_secret: docker_username
+    password:
+      from_secret: docker_password
+    dockerfile: Dockerfile
+    purge: true
+    repo: arminfriedl/lukewarm
+    tags: latest

README.md

@@ -1,3 +1,5 @@
+[![Build Status](https://drone.friedl.net/api/badges/container/lukewarm/status.svg)](https://drone.friedl.net/container/lukewarm)
+
 # Lukewarm and the Cool
 One day [Cool](https://en.wikipedia.org/wiki/Cool_(programming_language))
 compiled another