build image for arm64 as well

.drone.yml

@@ -1,6 +1,35 @@
 kind: pipeline
 type: docker
-name: Build
+name: linux-amd64
+
+platform:
+  os: linux
+  arch: amd64
+
+steps:
+  - name: publish
+    image: plugins/docker
+    settings:
+      username:
+        from_secret: docker_username
+      password:
+        from_secret: docker_password
+      repo: kichiyaki/caddy
+      auto_tag: true
+      dockerfile: Dockerfile
+
+trigger:
+  event:
+    - tag
+
+---
+kind: pipeline
+type: docker
+name: linux-arm64
+
+platform:
+  os: linux
+  arch: arm64
 
 steps:
   - name: publish