Add modern GNOME icon devkit

.gitmodules

@@ -6,3 +6,7 @@
 	path = source/icon-development-kit-www
 	url = https://gitlab.gnome.org/Teams/Design/icon-development-kit-www.git
 	update = none
+[submodule "source/icon-development-kit"]
+	path = source/icon-development-kit
+	url = https://gitlab.gnome.org/Teams/Design/icon-development-kit.git
+	update = none

Cargo.toml

@@ -50,5 +50,6 @@ default = []
 
 all = []
 # Enable entire icon kits
-icon-development-kit = []
+icon-development-kit-www = []
 fluent-system-icons = []
+icon-development-kit = []

README.md

@@ -34,15 +34,21 @@ You can browse the shipped icons using one of the following methods:
 
 For icons from the GNOME [icon-development-kit](https://gitlab.gnome.org/Teams/Design/icon-development-kit):
 + Install [Icon library](https://flathub.org/apps/details/org.gnome.design.IconLibrary)
-+ Browse the [GNOME icon resource](https://teams.pages.gitlab.gnome.org/Design/icon-development-kit-www/)
++ Browse the [GNOME icon resource](https://teams.pages.gitlab.gnome.org/Design/icon-development-kit/)
 
 For icons from [Fluent UI System Icons](https://github.com/microsoft/fluentui-system-icons):
 + Browse the [fluent icon library catalog](https://aka.ms/fluentui-system-icons)
 
+For icons from [the previous version of the GNOME development kit](https://gitlab.gnome.org/Teams/Design/icon-development-kit-www/):
++ Browse the [archived GNOME icon resource](https://web.archive.org/web/20250718142224/https://teams.pages.gitlab.gnome.org/Design/icon-development-kit-www/).
+
+Note that these legacy GNOME icons are
+[likely to be removed in a future update](https://github.com/Relm4/icons/issues/51#issuecomment-3539318240).
+
 For browsing all shipped icons:
 + Use the icon previews provided by in this repo: [16x16](icons16.md), [32x32](icons32.md) and [64x64](icons64.md)
 
-> Sometimes, icons-development-kit and Fluent UI System Icons have overlapping icon names, so the postfix "-alt" is added.
+> Some icons have overlapping icon names, so the postfix "-alt" is added.
 
 ### 2. Add Relm4 icons ✍
 
@@ -143,6 +149,7 @@ Existing icon sets can be updated as submodules with following commands:
 ```sh
 git submodule update --remote --checkout
 rm -rf build_icons/icons/fluentui-system-icons
+rm -rf build_icons/icons/icon-development-kit-www
 rm -rf build_icons/icons/icon-development-kit
 cd update_icons
 cargo run --bin fetch_icons
@@ -161,7 +168,7 @@ The source code of Relm4 icons is licensed under the terms of both the MIT licen
 
 ### Icons
 
-+ The icons in the `icons/icon-development-kit` folder are licensed under the terms of the [CC0 license](https://creativecommons.org/share-your-work/public-domain/cc0/) and therefore public domain.
++ The icons in the `icons/icon-development-kit` and `icons/icon-development-kit-www` folders are licensed under the terms of the [CC0 license](https://creativecommons.org/share-your-work/public-domain/cc0/) and therefore public domain.
 + The icons in the `icons/fluentui-system-icons` folder are licensed under the terms of the [MIT license](https://opensource.org/license/MIT/).
 
 Both licenses should work for both open source and proprietary applications (without warranty).