Mention schedule for commented-out cron

.github/workflows/download_providers.yml

 name: "Update oEmbed providers"
 on:
 #  schedule:
-#    - cron: "0 0 * * 2"
+#    - cron: "0 0 * * 2" # Every Tuesday at 00:00
   workflow_dispatch:
 jobs:
   update_providers: