Should newly published books be announced and described in Go Ressources, Announcements or Go Classifieds? Go Ressources might fit because journals are frequently announced there. Announcements might fit because it is an announcement. Go Classifieds does not seem to fit because messages there tend to be about trading used items.
Announcement seems ok, according to its description.
But i don’t see any problem to use one of the two others.
Go Resources and Announcements are both suitable categories for such announcements. Go Resources is for sharing Go resources, including publications related to learning Go, so it would make sense to post about a newly published book there. Also, Announcements is for users to announce Go-related events, news, and other developments, so posting about a new Go book would also be appropriate there.
As you mentioned, Go Classifieds is primarily intended for trading Go goods and services, so it wouldn’t be the best place to post about a new book.