docs/deprecated: update status for graphdriver-plugins

Add a mention of the feature being disabled by default, and
the DOCKERD_DEPRECATED_GRAPHDRIVER_PLUGINS env-var.

Signed-off-by: Sebastiaan van Stijn <[email protected]>

docs/deprecated.md

@@ -61,7 +61,7 @@ The table below provides an overview of the current status of deprecated feature
 | Removed    | [logentries logging driver](#logentries-logging-driver)                                                                            | v24.0      | v25.0  |
 | Removed    | [OOM-score adjust for the daemon](#oom-score-adjust-for-the-daemon)                                                                | v24.0      | v25.0  |
 | Removed    | [Buildkit build information](#buildkit-build-information)                                                                          | v23.0      | v24.0  |
-| Deprecated | [Legacy builder for Linux images](#legacy-builder-for-linux-images)                                                                | v23.0      | -      |
+| Deprecated | [Legacy builder for Linux images](#legacy-builder-for-linux-images)                                                      [deprecated.md](deprecated.md)          | v23.0      | -      |
 | Deprecated | [Legacy builder fallback](#legacy-builder-fallback)                                                                                | v23.0      | -      |
 | Removed    | [Btrfs storage driver on CentOS 7 and RHEL 7](#btrfs-storage-driver-on-centos-7-and-rhel-7)                                        | v20.10     | v23.0  |
 | Removed    | [Support for encrypted TLS private keys](#support-for-encrypted-tls-private-keys)                                                  | v20.10     | v23.0  |
@@ -152,6 +152,7 @@ part of the underlying image's Config, and deprecated:
 ### Graphdriver plugins (experimental)
 
 **Deprecated in Release: v27.0**
+**Disabled by default in Release: v27.0**
 **Target For Removal In Release: v28.0**
 
 [Graphdriver plugins](https://github.com/docker/cli/blob/v26.1.4/docs/extend/plugins_graphdriver.md)
@@ -160,6 +161,14 @@ storage drivers for storing images and containers. This feature was not
 maintained since its inception, and will no longer be supported in upcoming
 releases.
 
+Support for graphdriver plugins is disabled by default in v27.0, but an
+`DOCKERD_DEPRECATED_GRAPHDRIVER_PLUGINS` environment variable is provided
+to re-enable the feature. This environment-variable must be set in the daemon's
+environment, and set to a non-empty value.
+
+This environment variable will be removed in v28.0, and support for graphdriver
+plugins will be removed.
+
 Users of this feature are recommended to instead configure the Docker Engine
 to use the [containerd image store](https://docs.docker.com/storage/containerd/),
 and a custom [snapshotter](https://github.com/containerd/containerd/tree/v1.7.18/docs/snapshotters)