Build & doc issue

[vincent-j-zimmer]

[from Trammell Hudson on u-root Slack channel]
I tried building ModernFW and am not sure how to proceed with it. Built it with:

cd OvmfPkg
./build.sh -DDEBUG_ON_SERIAL_PORT=1```
Then I ran it in qemu with:
```qemu-system-x86_64 -serial stdio -bios ../Build/OvmfX64/DEBUG_GCC5/FV/OVMF.fd```
And it eventually dies with:
```ASSERT [DxeCore] /home/hudson/ModernFW/MdeModulePkg/Core/Dxe/Image/Image.c(1674): Image->Tpl == gEfiCurrentTpl```
(the docs don't have any build instructions, so I'm guessing at how to generate the rom image and run it)