Merge pull request oalders#3 from atoomic/schedule

only build on push to master and add a daily cron

.github/workflows/publish-to-docker.yml

@@ -1,7 +1,13 @@
 # https://github.com/marketplace/actions/publish-docker
 
 name: Publish to Docker
-on: [push]
+on:
+  push:
+    branches:
+      - 'master'
+  schedule:
+    - cron: '10 6 * * *'
+
 jobs:
   build:
     runs-on: ubuntu-latest