add drone

.drone.yml

@@ -0,0 +1,13 @@
+kind: pipeline
+name: default
+
+steps:
+- name: docker
+  image: plugins/docker
+  settings:
+    registry: r.sbruder.de
+    username:
+      from_secret: docker_username
+    password:
+      from_secret: docker_password
+    repo: r.sbruder.de/opentracker