cloud: Document how to download disk image

Now that it's being uploaded.

cloud/README.md

@@ -12,6 +12,41 @@ can be used in any virtualization/IaaS system that is
 such as [libvirt](https://blog.wikichoon.com/2020/09/virt-install-cloud-init.html),
 AWS, etc.
 
-- Download QCOW2: [Fedora ELN](https://storage.googleapis.com/centos-bootc-dev/fedora-bootc-cloud.qcow2).
+## Pre-generated disk images
 
-The qcow2 image was built using [osbuildbootc](https://github.com/cgwalters/osbuildbootc).
+There are pre-generated disk images available which can be launched directly.
+
+(Note: as of right now there are only disk images for Fedora until [this issue](https://github.com/osbuild/bootc-image-builder/issues/18) is fixed)
+
+The disk images are stored as OCI artifacts; currently in the Github container registry until
+[this issue](https://github.com/CentOS/centos-bootc-layered/issues/25) is fixed.
+
+### Unpacking the disk image using oras
+
+The [oras](https://oras.land/) project offers a handy CLI tool that can be used like this:
+
+```text
+$ oras pull ghcr.io/centos/fedora-bootc-cloud-disk:eln
+...
+Pulled ghcr.io/centos/fedora-bootc-cloud-disk:eln
+Digest: sha256:2bd73cc3589f6c7c28d7335a704133fd08526e4c0197a3ae038f1821c736c144
+$ zstd -d fedora-bootc-cloud-eln.qcow2.zst
+```
+
+### Unpacking using skopeo
+
+It's more common to have `skopeo` instead of `oras`, but unfortunately the ergonomics here are currently atrocious:
+
+```text
+$ skopeo copy docker://ghcr.io/centos/fedora-bootc-cloud-disk:eln oci:disk
+Getting image source signatures
+Copying blob da734940e022 done
+Copying config 44136fa355 done
+Writing manifest to image destination
+$ find disk/blobs/ -type f -size -5M | xargs -r rm
+$ mv disk/blobs/sha256/* fedora-bootc-cloud-eln.qcow2.zst
+$ rm -rf disk
+$ zstd -d fedora-bootc-cloud-eln.qcow2.zst
+fedora-bootc-cloud-eln.qcow2.zst: 790560768 bytes
+$
+```