Enable `arg_required_else_help`

[fu050409]

Such an error seems meaningless. It would be better to enable arg_required_else_help, so that when the user provides no arguments, the help information is displayed.

zerobrew on main [$?] via 🦀 v1.95.0
❯ zb
error: 'zb' requires a subcommand but one was not provided
  [subcommands: install, bundle, uninstall, migrate, list, info, doctor, gc, reset, init, completion, run, update, outdated, upgrade, help]

Usage: zb [OPTIONS] <COMMAND>

For more information, try '--help'.

zerobrew on main [$?] via 🦀 v1.95.0
❯ brew
Example usage:
  brew search TEXT|/REGEX/
  brew info [FORMULA|CASK...]
  brew install FORMULA|CASK...
  brew update
  brew upgrade [FORMULA|CASK...]
  brew uninstall FORMULA|CASK...
  brew list [FORMULA|CASK...]

Troubleshooting:
  brew config
  brew doctor
  brew install --verbose --debug FORMULA|CASK

Contributing:
  brew create URL [--no-fetch]
  brew edit [FORMULA|CASK...]

Further help:
  brew commands
  brew help [COMMAND]
  man brew
  https://docs.brew.sh

[fu050409]

Refer: clap-rs/clap#6397