Document setting minikube container runtime to docker explicitly

### Expected behavior

Since Kubernetes 1.24, the "docker" container runtime is no longer the default

This means that `minikube docker-env` _might_ no longer work, with the cluster,
unless it has been started with `minikube start --container-runtime=docker`

So this flag should be explicitly documented, in the **Quickstart** documentation.

### Actual behavior

`❌ Exiting due to MK_USAGE: The docker-env command is only compatible with the "docker" runtime, but this cluster was configured to use the "containerd" runtime.`

`❌ Exiting due to MK_USAGE: The docker-env command is only compatible with the "docker" runtime, but this cluster was configured to use the "crio" runtime.`

### Information

Docker is still available as a container runtime, but needs to be actively selected.

Kubernetes as a project is moving towards **only** supporting the CRI [standard](https://kubernetes.io/docs/concepts/architecture/cri/).
This means that "assuming" a Docker daemon is discouraged, preferring `crictl`.

Note that CRI is missing some Docker CLI commands, like `load` and `build`.

### Steps to reproduce the behavior

----

Related issues:

* #5613
* #5773
* #5739
* #5738

The same goes for other clusters, including installing the new `cri-dockerd` and `crictl`.

See https://kubernetes.io/blog/2020/12/02/dockershim-faq/

And https://www.mirantis.com/blog/mirantis-to-take-over-support-of-kubernetes-dockershim-2/