doc, leave a note about docopt in README

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
doc, show resulting struct yuck_s in README

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
doc, update README to reflect the new union-type

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, discuss the subcommand option case also

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>