Need to read the code for .Publish() to see how to construct the event struct for DM 

 It's KindEncryptedDirectMessage. This is the struct. nip4.go has encryption functions

ev := nostr.Event{
	PubKey:    pub,
	CreatedAt: nostr.Now(),
	Kind:      KindEncryptedDirectMessage,
	Tags:      nil,
	Content:   need to encrypt this,
}