Add docs PCI passthrough

[hiromu-a5a]

What this PR does / why we need it:

Added a document for PCI passthrough configuration on CAPK to avoid unnecessary trial and error. Although we can find a clue from KubeVirt document, to make the entire steps clear, would like to suggest adding the document to CAPK.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #192

Special notes for your reviewer: I think the release notes are not needed for this small change. If needed, please let me know.

Release notes:

NONE

[linux-foundation-easycla[bot]]

The committers listed above are authorized under a signed CLA.

• :white_check_mark: login: hiromu-a5a / name: Hiromu Asahina (475ad691da2ef59cb0f6439f4a31d7ed8eafa862)

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[agradouski]

/lgtm

[coveralls]

Pull Request Test Coverage Report for Build 3358702256

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 51.459%

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Totals
Change from base Build 3313966163:	0.0%
Covered Lines:	952
Relevant Lines:	1850

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💛 - Coveralls

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: davidvossel, hiromu-a5a

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kubernetes-sigs/cluster-api-provider-kubevirt/blob/main/OWNERS)~~ [davidvossel] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment