add usage example

README.md

@@ -30,7 +30,8 @@ chmod +x unbase_oci
 ./unbase_oci [options] base_image target_image output_image
 
 base_image, target_image, and output_image can either be OCI-archive file names
-or container images of the form "${container_engine}:${image}".
+or container images of the form "${container_engine}:${image}" where ${container_engine}
+might be `podman` or `docker`.
 For this the images must already be pulled in the local image storage of ${container_engine}.
 
 For all but base_image you can use the ":${tag}" shorthand to indicate that the same container engine
@@ -68,7 +69,19 @@ Options:
 
 ## Example Usage
 
-For instance, consider building a container on top of a Debian base. Let's assume `debian.oci` represents an exported OCI archive of the Debian base image, while `container.oci` is an exported OCI archive of the target image. To create a *bare* variant of the target container, containing only the dependencies of explicitly installed components on top of Debian (e.g.: libc), execute:
+For instance, consider building a container on top of a Debian base.
+Let's assume you build your container with a `Containerfile` based on the `debian` image.
+To create a *bare* variant of the target container, containing only the dependencies of explicitly installed components on top of Debian (e.g.: libc), execute:
+
+```shell
+podman pull debian
+podman build -t container .
+./unbase_oci --ldd-dependencies podman:debian podman:container:latest podman:container:bare
+```
+
+After running this command, the image `container:bare` is available in your local podman instance.
+
+If you work with exported oci archives, the equivalent command is:
 
 ```shell
 ./unbase_oci --ldd-dependencies debian.oci container.oci container_bare.oci