Add note on Docker storage driver:

Because hook-docker uses the overlay2
storage driver, the local docker client
using pull-images.sh must also use the
overlay2 storage driver.

Signed-off-by: Jacob Weinstock <[email protected]>

Author: jacobweinstock

README.md

@@ -168,6 +168,8 @@ For use cases where having container images already available in Docker is neede
 
 > Note: This will increase the overall size of HookOS. As HookOS is an in memory OS, make sure that the size increase works for the machines you are provisioning.
 
+> Note: Hook-docker uses the `overlay2` storage driver. For the `pull-images.sh` script to work, your local Docker storage driver must be `overlay2`.
+
 1. Create a file named `images.txt` in the [images/hook-embedded/](images/hook-embedded/) directory.
 1. Populate this `images.txt` file with the list of images to be embedded. See [images/hook-embedded/images.txt.example](images/hook-embedded/images.txt.example) for details on the required file format.
 1. Change directories to [images/hook-embedded/](images/hook-embedded/) and run [`pull-images.sh`](images/hook-embedded/pull-images.sh) script when building amd64 images and run [`pull-images.sh arm64`](images/hook-embedded/pull-images.sh) when building arm64 images. Read the comments at the top of the script for more details.