expand docs for ProvisioningRequest

[grosser]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

• instructions were missing the crd
• was unclear who needs to api flag
• had no examples how the request actually works

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

cc @yaroslava-serdiuk

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: grosser
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[k8s-ci-robot]

Hi @grosser. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[Shubham82]

/ok-to-test

[yaroslava-serdiuk]

Thanks for your change!
/lgtm

[grosser]

added, thx

[Shubham82]

Thanks @grosser
/lgtm