refactor(ci): add cron expression comment

Author: gekoke

.github/workflows/update.yaml

@@ -2,7 +2,8 @@ name: update
 on:
   workflow_dispatch:
   schedule:
-    - cron: '0 21 1 * *'
+    # At 00:00 on the 1st of every month
+    - cron: '0 0 1 * *' 
 
 jobs:
   update: