Add Drone CI

.drone.yml

@@ -0,0 +1,22 @@
+kind: pipeline
+name: default
+
+steps:
+- name: docker  
+  image: plugins/docker
+  settings:
+    context: app
+    dockerfile: app/Dockerfile
+    tags: 
+      - latest
+      - ${DRONE_TAG}
+    repo: jjtc/bookstack-ppm
+    username:
+      from_secret: docker_username
+    password:
+      from_secret: docker_password
+  when:
+    branch:
+      - master
+    event:
+      - tag