adds cron job to action

.github/workflows/publish.yml

@@ -1,7 +1,12 @@
 on:
+  # manually trigger
   workflow_dispatch:
+  # pushing to main
   push:
     branches: main
+  # every week on sunday
+  schedule:
+    - cron: "0 0 * * SUN"
 
 name: Quarto Publish