docs: Move the GIcon SECTION

Move it to the struct docs.

Signed-off-by: Philip Withnall <philip@tecnocode.co.uk>

Helps: #3037

docs/reference/gio/urlmap.js

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: LGPL-2.1-or-later
 // SPDX-FileCopyrightText: 2023 Matthias Clasen
 var baseURLs = [
+    [ 'GdkPixbuf', 'https://docs.gtk.org/gdk-pixbuf/' ],
     [ 'GLib', 'https://docs.gtk.org/glib/' ],
     [ 'GModule', 'https://docs.gtk.org/gmodule/' ],
     [ 'GObject', 'https://docs.gtk.org/gobject/' ],