nixos-artwork: fix gnome not adding wallpapers to list of backgrounds

pkgs/data/misc/nixos-artwork/wallpapers.nix

@@ -14,6 +14,22 @@ let
         mkdir -p $out/share/backgrounds/nixos
         ln -s $src $out/share/backgrounds/nixos/${src.name}
 
+        mkdir -p $out/share/gnome-background-properties/
+        cat <<EOF > $out/share/gnome-background-properties/${name}.xml
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE wallpapers SYSTEM "gnome-wp-list.dtd">
+<wallpapers>
+  <wallpaper deleted="false">
+    <name>${name}</name>
+    <filename>${src}</filename>
+    <options>zoom</options>
+    <shade_type>solid</shade_type>
+    <pcolor>#ffffff</pcolor>
+    <scolor>#000000</scolor>
+  </wallpaper>
+</wallpapers>
+EOF
+
         # TODO: is this path still needed?
         mkdir -p $out/share/artwork/gnome
         ln -s $src $out/share/artwork/gnome/${src.name}