docs: format external links

readme.md

@@ -165,7 +165,7 @@ Determines how the image set by wallpaper_filename is rendered. Possible values
 
 ## External Links
 
- * https://wiki.archlinux.org/index.php/Systemd/User
- * https://wiki.archlinux.org/index.php/Systemd/Timers
- * https://major.io/2015/02/11/rotate-gnome-3s-wallpaper-systemd-user-units-timers/
- * https://stackoverflow.com/questions/10374520/gsettings-with-cron
+ * [Gsettings with cron - Stack Overflow](https://stackoverflow.com/questions/10374520/gsettings-with-cron)
+ * [Rotate GNOME 3’s wallpaper with systemd user units and timers - Major Hayden](https://major.io/2015/02/11/rotate-gnome-3s-wallpaper-systemd-user-units-timers/)
+ * [systemd/Timers - ArchWiki](https://wiki.archlinux.org/index.php/Systemd/Timers)
+ * [systemd/User - ArchWiki](https://wiki.archlinux.org/index.php/Systemd/User)