Adjust help strings for options

[detsch]

Adjusted some of the text in help. This is what it looks like now:

aktualizr-lite command line options:
  -h [ --help ]         Print usage
  -v [ --version ]      Prints current aktualizr-lite version
  -c [ --config ] arg   Configuration file or directory path
  --loglevel arg        Set log level 0-5 (trace, debug, info, warning, error, 
                        fatal)
  --update-name arg     Name or version of the target to be used in pull, 
                        install, and update commands. default=latest
  --install-mode arg    Optional install mode. Supported modes: 
                        [delay-app-install]. By default both ostree and apps 
                        are installed before reboot
  --interval arg        Override uptane.polling_secs interval to poll for 
                        updates when in daemon mode
  --json arg            Output targets information as json when running check 
                        and list commands
  --src-dir arg         Directory that contains an offline update bundle. 
                        Enables offline mode for check, pull, install, and 
                        update commands
  --command arg         Command to execute: run, status, finalize, check, list,
                        install, pull, update, daemon