Update '.drone.yml'

.drone.yml

@@ -19,6 +19,16 @@ steps:
     - ls /drone/src/AOC2021.Test/bin/Debug/net5.0/
     - dotnet test AOC2021.Test --logger "console;verbosity=detailed"
 
+- name: docker-tag-demo
+  image: debian:stable-slim
+  commands:
+    - echo "The current branch is ${DRONE_BRANCH}"
+    - echo "The current commit hash is ${DRONE_COMMIT_SHA}"
+    - echo "The image tag is ${DRONE_BRANCH//\//-}-${DRONE_COMMIT_SHA:0:8}"
+    - echo "The url is $REGISTRY_URL"
+    - echo "The url is ${REGISTRY_URL}"
+    - echo "The url is $${REGISTRY_URL}"
+
 - name: build-aoc-2021-2
   image: plugins/docker
   settings: