update build doc

[ningmingxiao]

update build doc

[openshift-ci]

Hi @ningmingxiao. Thanks for your PR.

I'm waiting for a coreos 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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Details

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[gemini-code-assist]

Code Review

This pull request updates the build documentation, changing the cosa helper from a shell function to a standalone script to improve usability. It also introduces support for a NO_KVM environment variable for environments without nested virtualization. My feedback focuses on improving the documentation's clarity and correctness, including suggesting a more appropriate path for the script, clarifying the need for sudo, removing extraneous whitespace, and refining sentence structure for better readability.