add additional details for docker volumes in manifest

site/source/service-packaging/specification/docker.rst

@@ -48,9 +48,7 @@ In EmbassyOS, the mount specified in the Manifest gets bound to ``/embassy-data/
 Volumes
 -------
 
-Each service application gets one or more volumes allocated to it by EmbassyOS. All service application data is stored in this directory and is persisted across updates.
-
-This is also defined in the Manifest in the volumes section:
+Volumes are the mechanism for persisting data generated by and used by Docker containers. In EmbassyOS, services can declare as one or many volumes in the Manifest:
 
 .. code:: yaml
 
@@ -59,6 +57,41 @@ This is also defined in the Manifest in the volumes section:
         main:
             type: data
 
+Volume Types
+^^^^^^^^^^^^
+1. ``data`` - A volume to persist application data. All service application data is stored in this directory and is persisted across updates.
+2. ``assets`` - A volume to store miscellaneous assets that do not need to be in the main image. 
+
+If an asset volume is specified, there must exist a folder entitled assets, and a subfolder entitled the name of the asset volume:
+
+.. code-block::
+
+    :emphazize-lines: 9,10,11,16,17
+
+        properties:
+            type: docker
+            image: compat
+            system: true
+            entrypoint: compat
+            args:
+                - properties
+                - /root
+            mounts:
+                main: /root
+                compat: /mnt/assets
+
+        volumes:
+            # This is the image where files from the project asset directory will go
+            main:
+                type: data
+            compat:
+                type: assets
+
+        # required project folder structure
+        ├── assets
+        │   └── compat
+
+
 .. warning:: Any files in the mounted volume path will be overwritten when a backup restore occurs.
 
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