systemd user units must have WantedBy=default.target

Using WantedBy=multi-user.target might work to start the unit at
boot-up, but the unit will not be started in other contexts such as
"systemctl restart user@<id>.service" which is useful in to restart
user services identified by needrestart.

From https://wiki.archlinux.org/title/systemd/User#How_it_works :

> When a systemd user instance starts, it brings up the per user target
default.target.

howto/irc.md

@@ -401,7 +401,7 @@ also start it now. Finally we verify it is loaded and actively running.
     ExecStart=/usr/bin/znc --foreground
     
     [Install]
-    WantedBy=multi-user.target
+    WantedBy=default.target
     ircbouncer@chives:~$ systemctl --user enable --now znc
     Created symlink /home/ircbouncer/.config/systemd/user/multi-user.target.wants/znc.service → /home/ircbouncer/.config/systemd/user/znc.service.
     ircbouncer@chives:~$ systemctl --user status znc