help message
```
$ topcron -h
topcron 0.1.3
A Cron log parser and viewer.

To see status and duration of cronjobs, please add `-L 15` to EXTRA_OPTS of cron, then restart the
daemon.

USAGE:
    topcron [OPTIONS]

OPTIONS:
    -0, --ok-filter                    Display only successfull cronjobs
    -1, --ko-filter                    Display only failed cronjobs (include unknow status)
    -f, --file <FILE>                  File(s) to parse [default: /var/log/syslog]
    -F, --filter <FILTER>              Filter (user, pid, command...) specific cronjobs [default: ]
    -h, --help                         Print help information
    -t, --timestamp-mode               Display dates and duration in timestamp format
    -T, --truncate-mode                Don't truncate command line
    -u, --user-filter <USER_FILTER>    Filter (user, pid, command...) specific cronjobs [default: ]
    -v, --verbose                      Show debug messages
    -V, --version                      Print version information

```