Update minikube instructions with recent changes

[cwilkers]

What this PR does / why we need it

Recent changes in minikube have broken our quickstart in two places:

• https://github.com/kubernetes/minikube/issues/15918
• https://github.com/kubevirt/kubevirt.github.io/issues/859

A documentation fix was found for #859 where we add a CNI to make masquerade VMs work.

An issue has been filed against minikube because a missing curl command has broken the kubevirt addon.

[jobbler]

/lgtm

[cwilkers]

Thanks for the review!

/approve

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cwilkers

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