Documentation: Add LWN.net article

Contributed by Valentine Sinitsyn under CC-BY-SA.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Valentine Sinitsyn <valentine.sinitsyn@gmail.com>
Documentation: Describe memory layout of Jailhouse

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>