Correct documentation for UEFI secure boot to remove statement that chainloader does not work with secure boot. This was fixed by the commit 6d05264 (kern/efi/sb: Add chainloaded image as shim's verifiable object). Fixes: https://savannah.gnu.org/bugs/?62004 Signed-off-by: Andrew Hamilton <adhamilt@gmail.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>