nixos/doc/manual/release-notes/rl-2511: add sing-box

Author: Prince213

nixos/doc/manual/release-notes/rl-2511.section.md

@@ -103,6 +103,9 @@
 - The non-LTS Forgejo package (`forgejo`) has been updated to 12.0.0. This release contains breaking changes, see the [release blog post](https://forgejo.org/2025-07-release-v12-0/)
   for all the details and how to ensure smooth upgrades.
 
+- `sing-box` has been updated to 1.12.3, which includes a number of breaking changes, old configurations may need updating or they will cause the tool to fail to run.
+  See the [change log](https://sing-box.sagernet.org/changelog/#1123) for details and [migration](https://sing-box.sagernet.org/migration/#1120) for how to update old configurations.
+
 - The Pocket ID module ([`services.pocket-id`][#opt-services.pocket-id.enable]) and package (`pocket-id`) has been updated to 1.0.0. Some environment variables have been changed or removed, see the [migration guide](https://pocket-id.org/docs/setup/migrate-to-v1/).
 
 - The `zigbee2mqtt` package was updated to version 2.x, which contains breaking changes. See the [discussion](https://github.com/Koenkk/zigbee2mqtt/discussions/24198) for further information.