Added format of crontab file

pages/common/crontab.md

@@ -13,3 +13,16 @@
 - Remove all cron jobs for the current user:
 
 `crontab -r`
+
+- Configuration file:
+
+```
+# ┌───────────── min (0 - 59)
+# │ ┌────────────── hour (0 - 23)
+# │ │ ┌─────────────── day of month (1 - 31)
+# │ │ │ ┌──────────────── month (1 - 12)
+# │ │ │ │ ┌───────────────── day of week (0 - 6) (0 to 6 are Sunday to Saturday, or use names; 7 is Sunday, the same as 0)
+# │ │ │ │ │
+# │ │ │ │ │
+# * * * * *  command to execute
+```