[docs] UPDATING: document upgrade to NC 25.0.4

Along with the newly supported dd.conf variables and the docker image
rework.

UPDATING.md

@@ -24,6 +24,40 @@ little to no impact.
 
 ## 2023
 
+### 2023-03 - Nextcloud 25.0.4 + NC Docker rework
+
+Update version to 25.0.4 and rework its docker image.
+
+The image now manages volumes and configuration in a better fashion,
+thanks to that we achieve an image that is closer to the original one, but
+gets the plugins that we want and the configuration that we want for
+integration with DD.
+
+You can now define `BBB_HOST` and `BBB_API_SECRET` as variables in dd.conf,
+which are used to configure the corresponding plugin on Nextcloud.
+
+You can also define a list of custom plugins to enable/disable in Nextcloud
+with the dd.conf variables: `NEXTCLOUD_PLUGINS_ENABLE`,
+`NEXTCLOUD_PLUGINS_DISABLE`. See `dd.conf.sample` for more information.
+
+If upgrading from previous versions, you probably will want to check the
+permissions assigned to the `user_saml` plugin directory.
+You can also force its reinstallation with proper permissions with:
+
+    # Usually SRC_FOLDER in dd.conf is /opt/DD/src
+    rm -rf "${SRC_FOLDER:-/opt/DD/src}/nextcloud/custom_apps/user_saml/"
+    # Restart the NC container (only if previous command runs after upgrade)
+    # docker-compose restart dd-apps-nextcloud-app
+
+
+Upgrade from a commit that includes Nextcloud major version 24 (see previous
+UPGRADE messages) with:
+
+    # Upgrade to NC version 24.0.10 (latest 24 minor on 2023-03-14)
+    ./dd-ctl update a27f44262b9e4d37b21265a20575e8aa2dd78cb0
+    # Upgrade to NC version 25.0.4  (latest 25 minor on 2023-03-14)
+    ./dd-ctl update 7e2c748f51674968719f5abbf442477678d614c7
+
 ### 2023-02 - Nextcloud 24.0.10
 
 Update version to 24.0.10