Add Dockerfile and drone build instructions

.drone.yml

@@ -7,3 +7,17 @@ steps:
     image: python:3-alpine
     commands:
       - python3 -m unittest
+
+  - name: build
+    image: plugins/docker
+    settings:
+      registry: docker.dietrich-rink.de
+      repo: docker.dietrich-rink.de/drone-test
+      auto_tag: true
+      username:
+        from_secret: registry_user
+      password:
+        from_secret: registry_pass
+    when:
+      event:
+        - tag