docs: added cross-arch support in FAQ
docs: added cross-arch support in FAQ

Actually mentioned the lack of cross-architecture emulation support
between the host and guest systems in FAQ.md

Signed-off-by: George Pisaltu <084beef259e7feee20f091a1c4e2b24ee6aa34bb@amazon.com>

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