[PATCH] doc: add deprecation notice for kni example

[Thomas Monjalon]

30/06/2022 18:50, Bruce Richardson:
> +* examples/kni: The ``kni`` kernel module and library are not recommended for use by new applications -
> +  other technologies such as virtio-user are recommended instead.
> +  Because of this, the example application for kni is deprecated and will be removed in a future release.

Acked-by: Thomas Monjalon <thomas at monjalon.net>

I think it would have been better to give a precise timeline.