nitro_enclaves: Update documentation for Arm64 support

Add references for hugepages and booting steps for Arm64.

Include info about the current supported architectures for the
NE kernel driver.

Reviewed-by: George-Aurelian Popescu <popegeo@amazon.com>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Andra Paraschiv <andraprs@amazon.com>
Link: https://lore.kernel.org/r/20210827154930.40608-3-andraprs@amazon.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>