config/date-time: warn that rc.conf TIMEZONE should be removed when linking

Author: classabbyamp

src/config/date-time.md

@@ -11,6 +11,8 @@ The default system timezone can be set by linking the timezone file to
 ```
 # ln -sf /usr/share/zoneinfo/<timezone> /etc/localtime
 ```
+> Note: If the variable `TIMEZONE` is set in `/etc/rc.conf`, it should be removed
+> or commented out, as this will override what has been set with `ln` on reboot.
 
 To change the timezone on a per user basis, the `TZ` variable can be exported
 from your shell's profile: