board/pc: add documentation for testing with qemu

Add some documentation about running the pc defconfigs in qemu.
In particular, document the use of the -bios parameter to use the OVMF
firmware to test the UEFI image.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/pc/readme.txt

@@ -35,3 +35,44 @@ Bare PC sample config
   the setup as well.
 
 3. Enjoy
+
+Emulation in qemu (BIOS)
+========================
+
+1. Edit grub-bios.cfg
+
+  Since the driver will show up in the virtual machine as /dev/vda,
+  change board/pc/grub-bios.cfg to use root=/dev/vda2 instead of
+  root=/dev/sda2. Then rebuild grub2 and the image.
+
+2. Run the emulation with:
+
+qemu-system-x86_64 \
+	-M pc \
+	-drive file=output/images/disk.img,if=virtio,format=raw \
+	-net nic,model=virtio \
+	-net user
+
+
+Emulation in qemu (UEFI)
+========================
+
+1. Edit grub-efi.cfg
+
+  Since the driver will show up in the virtual machine as /dev/vda,
+  change board/pc/grub-efi.cfg to use root=/dev/vda2 instead of
+  root=/dev/sda2. Then rebuild grub2 and the image.
+
+2. Run the emulation with:
+
+qemu-system-x86_64 \
+	-M pc \
+	-bios </path/to/OVMF_CODE.fd> \
+	-drive file=output/images/disk.img,if=virtio,format=raw \
+	-net nic,model=virtio \
+	-net user
+
+Note that </path/to/OVMF.fd> needs to point to a valid x86_64 UEFI
+firmware image for qemu. It may be provided by your distribution as a
+edk2 or OVMF package, in path such as
+/usr/share/edk2/ovmf/OVMF_CODE.fd .