Issues in the qemu docs

1. When started with the parameter "-BIOS ${OVMF_PATH}", the qemu screen is black and doesn't show the AGl home screen. I remove the parameter of ovmf and AGL homescreen display successfully.

2. The AGL interface mouse in the virtual machine is inconsistent with the outside mouse. we can use parameter "-usbdevice tablet" to solve it, but the parameter is deprecated, I will investigate it later.

3. It's better to add the following info to the docs:

Refer:

     https://docs.automotivelinux.org/docs/en/master/getting_started/reference/getting-started/machines/qemu.html

logs: