add note about DOCKER_HOST for kn quickstart kind

[psschwei]

Fixes knative-extensions/kn-plugin-quickstart#617

Proposed Changes

Adds a snippet about setting DOCKER_HOST if running kn quickstart kind against a non-standard docker endpoint.

[netlify]

✅ Deploy Preview for knative ready!

Name	Link
🔨 Latest commit	68458f6
🔍 Latest deploy log	https://app.netlify.com/projects/knative/deploys/6a0f693096a2880c0f033c91
😎 Deploy Preview	https://deploy-preview-6643--knative.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[psschwei]

looks like this got rate limited

9:22:01 PM:   File "/opt/buildhome/.local/share/mise/installs/python/3.13.13/lib/python3.13/site-packages/github/Requester.py", line 378, in __check
9:22:01 PM:     raise self.__createException(status, responseHeaders, output)
9:22:01 PM: github.GithubException.RateLimitExceededException: 403 {"message": "API rate limit exceeded for 3.21.168.160. (But here's the good news: Authenticated requests get a higher rate limit. Check out the documentation for more details.)", "documentation_url": "https://docs.github.com/rest/overview/resources-in-the-rest-api#rate-limiting"}

[dprotaso]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, psschwei

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [dprotaso]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment