doc: update FAQ to stop saying we dont have ACPI

We support ACPI nowadays. It doesn't change anything about this FAQ
entry, because we don't implement power management using ACPI, but it
still needs to be updated to actually say that.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

FAQ.md

@@ -196,9 +196,9 @@ mapping:
 
 ### How can I gracefully reboot the guest? How can I gracefully poweroff the guest?
 
-Firecracker does not implement ACPI and PM devices, therefore operations like
-gracefully rebooting or powering off the guest are supported in unconventional
-ways.
+Firecracker does not virtualize guest power management, therefore operations
+like gracefully rebooting or powering off the guest are supported in
+unconventional ways.
 
 Running the `poweroff` or `halt` commands inside a Linux guest will bring it
 down but Firecracker process remains unaware of the guest shutdown so it lives