Add prerequisites to readme

[csabakecskemeti]

What does this PR do?

Extend readme start lorax section with nvidia-container-toolkit prerequisites

Fixes # (issue)
Documentation missing detail

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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  to it if that's the case.
• Did you write any new necessary tests?

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[tgaddair]

Thanks for the PR!