chore(doc): Update kfp-kubenetes release instructions.

[chensun]

Description of your changes:

Checklist:

• [ ] You have signed off your commits
• [ ] The title for your pull request (PR) should follow our title convention. Learn more about the pull request title convention used in this repository.

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hbelmiro

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: - ~~[kubernetes_platform/OWNERS](https://github.com/kubeflow/pipelines/blob/master/kubernetes_platform/OWNERS)~~ [hbelmiro] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[chensun]

/unhold