Add default help message

[tannerwelsh]

Running codeunion without giving a proper subcommand throws an error. -1 UX.

This is a quick attempt to remedy that:

$ codeunion
Usage: codeunion <command>

The CodeUnion command-line tool is meant to be used in conjunction with CodeUnion's curriculum.

Think of it as your "learning sherpa."

Commands:
    config
    examples
    feedback
    projects
    search

Options:
    -h, --help                       Print this help message

[tannerwelsh]

Ideal would be to show a summary of each command in the message too, but wondering where that information should live.

Thoughts @zspencer / @jfarmer ?

[zspencer]

For now, it makes sense to just include it here, though at some point we should consider having a standard interface for getting a command's terse help description. Something like codeunion config -h -t or something so we can auto-discover all the commands and get their short descriptions.

[zspencer]

👍 on the code, etc.

[tannerwelsh]

Thanks, @zspencer. I agree w/ your first comment so created #36.