bib: document local containers

README.md

@@ -46,6 +46,33 @@ sudo podman run \
     quay.io/centos-bootc/fedora-bootc:eln
 ```
 
+### Using local containers
+
+To use containers from local container's storage rather than a registry, we need to ensure two things:
+- the container exists in local storage
+- mount the local container storage
+
+Since the container is run in `rootful` only root container storage paths are allowed.
+
+```bash
+sudo podman run \
+    --rm \
+    -it \
+    --privileged \
+    --pull=newer \
+    --security-opt label=type:unconfined_t \
+    -v $(pwd)/config.json:/config.json \
+    -v $(pwd)/output:/output \
+    -v /var/lib/containers/storage:/var/lib/containers/storage \
+    quay.io/centos-bootc/bootc-image-builder:latest \
+    --type qcow2 \
+    --config /config.json \
+    -- local \
+    localhost/bootc:eln
+```
+
+Note we need to pass the `--local` flag, we need to mount the storage path as a volume and then use the name of the local container.
+
 ### Running the resulting QCOW2 file on Linux (x86_64)
 
 A virtual machine can be launched using `qemu-system-x86_64` or with `virt-install` as shown below.