Add kernel requirement for connect-usb.md

[mattwojo]

Resolves https://github.com/MicrosoftDocs/WSL/pull/1950

[learn-build-service-prod[bot]]

Learn Build status updates of commit 168fb82:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
WSL/connect-usb.md	:white_check_mark:Succeeded	View

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