Add volume documentation.

docs/config/image.rst

@@ -484,3 +484,17 @@ allowing the image directory structure to be preserved;
 this would be useful for application paths that
 use directories to store runtime state,
 such as ``/var/lib/nginx`` for ``nginx``.
+
+
+Volumes: ``volumes``
+====================
+
+Paths in the image that should be mounted read write into the container
+from user defined directories.
+
+This is used for read-only containers to
+write out data that should be persisted, such as ``postgres`` data.
+
+If a volume is not defined during container creation,
+``sponson`` creates a directory for the volume
+to ensure the container works as expected.

docs/usage/container.rst

@@ -31,7 +31,7 @@ new
 
 .. code::
 
-    sponson container new [--version <image version>] [--readwrite] <image name> <new container name>
+    sponson container new [--version <image version>] [--volume <volume name>:<volume source path>]* [--readwrite] <image name> <new container name>
 
 
 Create a new container based on the provided image name.
@@ -41,6 +41,11 @@ The container name must be unique.
 The latest version of the image is used as a base for the container,
 unless ``--version`` provides a specific version.
 
+Volumes can be defined for this container using the ``--volume`` option.
+The argument should be of the form ``<volume name>:<volume source path>``.
+
+``--volume`` can be defined multiple times for each volume in the container.
+
 Containers are by default read-only,
 however if ``--readwrite`` is specified the container is writable,
 and any changes made by the container are stored in