docs: add Spectre-BHB recommendations
docs: add Spectre-BHB recommendations

Signed-off-by: Diana Popa <4240422768c1b315e51818a074064501037757cd@amazon.com>
Signed-off-by: alindima <120e67a722c5477956e37ee6f342b2830138960b@amazon.com>

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker