Update config-example.md

[xLexih]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

The config-example.md has information for the registry but doesn't assign a node for it.

Added a registry node to improve clarity so people don't miss the potential option.

Which issue(s) this PR fixes:

config-example.md

Special notes for reviewers:

Does this PR introduced a user-facing change?

None

Additional documentation, usage docs, etc.:

docs/registry.md

[kubesphere-prow[bot]]

Welcome @xLexih! It looks like this is your first PR to kubesphere/kubekey 🎉

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[redscholar]

/approve /lgtm

[kubesphere-prow[bot]]

LGTM label has been added.

Git tree hash: dc29d0f498042f586dac3c3fdd8785d12c54e260

[liangzai006]

/lgtm

[pixiake]

/approve

[kubesphere-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: pixiake, redscholar, xLexih

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

The pull request process is described here

Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kubesphere/kubekey/blob/master/OWNERS)~~ [pixiake] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[pixiake]

@all-contributors please add @xLexih for doc

[allcontributors[bot]]

@pixiake

I've put up a pull request to add @xLexih! :tada: