Update cron scaler documentation to clarify the cron (kedacore#514)

Signed-off-by: jorturfer <[email protected]>

content/docs/2.5/scalers/cron.md

@@ -27,7 +27,9 @@ triggers:
 - `timezone` - One of the acceptable values from the IANA Time Zone Database. The list of timezones can be found [here](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones)
 - `start` - Cron expression indicating the start of the cron schedule.
 - `end` - Cron expression indicating the end of the cron schedule.
-- `desiredReplicas` - Number of replicas to which the resource has to be scaled between the start and end of the cron schedule.
+- `desiredReplicas` - Number of replicas to which the resource has to be scaled **between the start and end** of the cron schedule.
+
+> 💡 **Note:** `start`/`end` support ["Linux format cron"](https://en.wikipedia.org/wiki/Cron) (Minute Hour Dom Month Dow).
 
 > **Notice:**
 > **Start and end should not be same.**