help: print cli/parser help message if used

[dawidd6]

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External commands using cli/parser currently can't produce a valid help message, because brew looks for #: comments on top of the command file. With this patch, it becomes possible to get the help message normally.

Discussion on the issue here: https://github.com/Homebrew/homebrew-linux-dev/pull/137

[issyl0]

Thanks, Dawid! This works for me. Here's the before/after:

$ cd $(brew --repo homebrew/linux-dev)
$ hub pr checkout 137
$ brew build-bottle-pr --help
  Warning: No help text in: /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-linux-dev/cmd/brew-build-bottle-pr.rb
  Example usage:
    brew search [TEXT|/REGEX/]
  [...]

$ cd $(brew --repo)
$ hub pr checkout 6965
$ brew build-bottle-pr --help
  Usage: brew build-bottle-pr [--remote=user] [--dry-run] [--verbose] [--tap-dir] [--force] Submit a pull request to build a bottle for a formula.
  [...]

[MikeMcQuaid]

Nice work, we should definitely do something like this.

[MikeMcQuaid]

Thanks @dawidd6!