Use a composite action

This is an attempt to see if this is faster than a Go action.

README.md

@@ -0,0 +1,2 @@
+# Watchtower Action
+This action will automatically trigger an update of watchtower, causing containers that have the label `com.centurylinklabs.watchtower.enable=true` to be automatically updated.

action.yml

@@ -1,5 +1,8 @@
 name: 'Watchtower Update'
 description: 'Automatically triggers Watchtower to scan for new images'
 runs:
-  using: 'go'
+  using: 'composite'
-  main: 'main.go'
+  steps:
+    - name: Trigger Watchtower Update
+      run: |
+        curl -H "Authorization: Bearer mytoken" https://watchtower.seeseepuff.be/v1/update