Add Katib webhook documentation

[andreyvelich]

Fixes: #1266.

I added Katib webhook documentation.

/cc @connorlwilkes @kylepad @gaocegege @johnugeorge @yanniszark

[google-oss-robot]

@andreyvelich: GitHub didn't allow me to request PR reviews from the following users: kylepad, connorlwilkes.

Note that only kubeflow members and repo collaborators can review this PR, and authors cannot review their own PRs.

In response to this:

Fixes: #1266.

I added Katib webhook documentation.

/cc @connorlwilkes @kylepad @gaocegege @johnugeorge @yanniszark

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andreyvelich

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 [andreyvelich]

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

[johnugeorge]

/lgtm