improve: add example in help command

[hiro08gh]

For example.

A simple alias manager for multiple shells

Usage: alx <COMMAND>

Commands:
  init     Initialize alx configuration
  add      Add a new alias
  remove   Remove one or more aliases
  list     List all aliases
  search   Search aliases by keyword
  edit     Edit an alias
  export   Export aliases to a file
  import   Import aliases from a file
  groups   Show all available groups
  info     Show information about alx
  migrate  Migrate aliases from shell configuration file
  help     Print this message or the help of the given subcommand(s)

Options:
  -h, --help     Print help
  -V, --version  Print version

EXAMPLES:
    alx add ll 'ls -la' -d 'List all files with details'
    alx list -g dev
    alx search git
    alx remove temp-alias
    alx export -o aliases.json

For more information on a specific command, use: alx <COMMAND> --help