set up cron to run twice a month

.github/workflows/update-index.yml

@@ -1,9 +1,8 @@
 name: Update index.html
 
 on:
- #schedule:
-    # Run once every 5 minutes (GitHub Actions' minimum interval)
-   # - cron: "*/5 * * * *"
+  schedule:
+    - cron: "0 0 1,15 * *"  # Runs at 00:00 on the 1st and 15th of every month
   push:
     branches: 
       - master  # Trigger the workflow on push to the master branch