See https://developer.gnome.org/hig/stable/typography.html https://bugzilla.gnome.org/show_bug.cgi?id=772211
Position the explanatory text below the actual option and tweak whitespace a bit. https://bugzilla.gnome.org/show_bug.cgi?id=730843
This continues turning "example" in a real gnome-shell extension tutorial, showing how to create GSettings using Convenience and how to build a simple preference dialog by subclassing GtkGrid and binding GObject properties to GSettings.