docs: Recommend installing vmnet-helper from Homebrew on macOS 26

[nirs]

Update the docs for vfkit and krunkit to recommend installing vmnet-helper from Homebrew. This is easy to install, avoids the sudo configuration and ensures that you never run vmnet-helper as root when it is not needed.

Issues:

• Work only on macOS 26, so complicates the install a little bit.

Example docs from vmnet-helper doing the same:
https://github.com/nirs/vmnet-helper?tab=readme-ov-file#installation

[k8s-triage-robot]

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This bot triages un-triaged issues according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
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/lifecycle stale

[k8s-triage-robot]

The Kubernetes project currently lacks enough active contributors to adequately respond to all issues.

This bot triages un-triaged issues according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
• After 30d of inactivity since lifecycle/rotten was applied, the issue is closed

You can:

• Mark this issue as fresh with /remove-lifecycle rotten
• Close this issue with /close
• Offer to help out with Issue Triage

Please send feedback to sig-contributor-experience at kubernetes/community.

/lifecycle rotten

[nirs]

/remove-lifecycle rotten
/lifecycle frozen