CLI should give defaults in help

[anjiro]

When dicy on the CLI prints the help message, it helpfully lists the type of option expected ([string]) and the valid selections ([choices: "dvi", "pdf", "ps", "svg"]) but not what the default is for each option. It should indicate which choice is the default if no option is passed by the user.

[yitzchak]

Thanks for the feedback! I'll look into it.