pub fn command() -> CommandExpand description
The command tree this binary parses with, and the one every reader takes.
Cli::command is the derived half and carries the grammar alone. This
function is what puts the words on it, and every word it puts there comes
out of headwater_verbs::VERBS: the group headings and the one-line
summary of the first screen, the long description a verb prints for itself,
and the same pair for each second word.
main prints help through this and tests/verbs.rs walks it, so a reader
of the help and a reader of the test meet the same tree. A caller that used
Cli::command directly would meet a tree with no prose on it at all.