doc, brag about scmver feature

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
doc, also describe yuck genman briefly

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
import xmpl-subcommands.html for the man page example

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