Add short and long help messages

[volks73]

The clap crate supports short and long help messages. When the -h flag is used, the short help messages are displayed. When the --help flag is used, the long help messages are displayed. The short help message would be a brief sentence to "remind" the user of the argument's purpose. The long help message would be a detailed explanation of the argument's purpose. Currently, the help message are on the long side and shorter versions could be appreciated.