docs: add manpage for import-layer

Add the missing manpage for the subcommand import-layer.

Signed-off-by: Silvano Cirujano Cuesta <silvano.cirujano-cuesta@siemens.com>

docs/containers-storage-import-layer.md

@@ -0,0 +1,76 @@
+## containers-storage-import-layer 1 "April 2019"
+
+## NAME
+containers-storage import-layer - Import files to a new layer
+
+## SYNOPSIS
+**containers-storage** **import-layer** [*options* [...]] [*parentLayerNameOrID*]
+
+## DESCRIPTION
+This subcommand is a combination of *containers-storage create-layer* and
+*containers-storage apply-diff*.
+
+When a layer is first created with *containers-storage create-layer*, it
+contains no changes relative to its parent layer.
+The layer can either be mounted read-write and its contents modified
+directly, or contents can be added (or removed) by applying a layer diff
+by running *containers-storage apply-diff*.
+
+## OPTIONS
+**-n** *name*
+
+Sets an optional name for the layer. If a name is already in use, an error is
+returned.
+
+**-i | --id** *ID*
+
+Sets the ID for the layer. If none is specified, one is generated.
+
+**-f | --file** *filename*
+
+Specifies the name of a file from which the diff should be read. If this
+option is not used, the diff is read from standard input.
+
+**-l | --label** *mount-label*
+
+Sets the label which should be assigned as an SELinux context when mounting the
+layer.
+
+**-r | --readonly**
+
+Mark the layer as readonly.
+
+**-j | --json**
+
+Prefer JSON output.
+
+**--uidmap**
+
+UID map specified in the format expected by *subuid*. It cannot be specified simultaneously with *--hostuidmap*.
+
+**--gidmap**
+
+GID map specified in the format expected by *subgid*. It cannot be specified simultaneously with *--hostuidmap*.
+
+**--hostuidmap**
+
+Force host UID map. It cannot be specified simultaneously with neither *--uidmap* nor *--subuidmap*.
+
+**--hostgidmap**
+
+Force host GID map. It cannot be specified simultaneously with neither *--gidmap* nor *--subgidmap*.
+
+**--subuidmap** *username*
+
+Create UID map for username using the data from /etc/subuid. It cannot be specified simultaneously with *--hostuidmap*.
+
+**--subgidmap** *group-name*
+
+Create GID map for group-name using the data from /etc/subgid. It cannot be specified simultaneously with *--hostuidmap*.
+
+## EXAMPLE
+**containers-storage import-layer -f 71841c97e320d6cde.tar.gz -n new-layer somelayer**
+
+## SEE ALSO
+containers-storage-create-layer(1)
+containers-storage-apply-diff(1)