Add order-only dependency on `doc/xhtml` creation
Add order-only dependency on `doc/xhtml` creation

https://www.gnu.org/software/make/manual/html_node/Prerequisite-Types.html

newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat