docs(demo): add line to OSM automated demo docs
Clarifies the need to update CTR_REGISTRY in the .env environment
variable file when using a remote Kubernetes cluster for the OSM
automated demo.
- `brew install kind` on macOS
- Provision a local cluster and registry in Docker: `make kind-up`
- **Option 2:** A Kubernetes cluster - use an already provisioned cluster config, either in the default location ($HOME/.kube/config) or referenced by the $KUBECONFIG environment variable.
+ - Set `CTR_REGISTRY` in your `.env` file to a container registry you have permission to push and pull from.
+ - Ensure you are logged into the container registry using: `docker login <registry url>`
We will use images from [Docker Hub](https://hub.docker.com/r/openservicemesh/osm-controller). Ensure you can pull these containers using: `docker pull openservicemesh/osm-controller`
