OvmfPkg/RiscVVirt: Add a readme for build and test

Add a readme file which provides information regarding how
to build and test EDK2 on RISC-V qemu virt platform.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Andrei Warkentin <andrei.warkentin@intel.com>
Cc: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

OvmfPkg/RiscVVirt/README.md

@@ -0,0 +1,49 @@
+# Support for RISC-V QEMU virt platform
+
+## Overview
+RISC-V QEMU 'virt' is a generic platform which does not correspond to any real
+hardware.
+
+EDK2 for RISC-V virt platform is a payload (S-mode) for the previous stage M-mode
+firmware like OpenSBI. It follows PEI less design.
+
+The minimum QEMU version required is
+**[8.1](https://wiki.qemu.org/Planning/8.1)** or with commit
+[7efd65423a](https://github.com/qemu/qemu/commit/7efd65423ab22e6f5890ca08ae40c84d6660242f)
+which supports separate pflash devices for EDK2 code and variable storage.
+
+## Build
+    export WORKSPACE=`pwd`
+    export GCC5_RISCV64_PREFIX=riscv64-linux-gnu-
+    export PACKAGES_PATH=$WORKSPACE/edk2
+    export EDK_TOOLS_PATH=$WORKSPACE/edk2/BaseTools
+    source edk2/edksetup.sh
+    make -C edk2/BaseTools
+    source edk2/edksetup.sh BaseTools
+    build -a RISCV64 --buildtarget RELEASE -p OvmfPkg/RiscVVirt/RiscVVirtQemu.dsc -t GCC5
+
+## Test
+Below example shows how to boot openSUSE Tumbleweed E20.
+
+1) RISC-V QEMU pflash devices should be of of size 32MiB.
+
+    `truncate -s 32M Build/RiscVVirtQemu/RELEASE_GCC5/FV/RISCV_VIRT_CODE.fd`
+
+    `truncate -s 32M Build/RiscVVirtQemu/RELEASE_GCC5/FV/RISCV_VIRT_VARS.fd`
+
+2) Running QEMU
+
+        qemu-system-riscv64 \
+        -M virt,pflash0=pflash0,pflash1=pflash1,acpi=off \
+        -m 4096 -smp 2 \
+        -serial mon:stdio \
+        -device virtio-gpu-pci -full-screen \
+        -device qemu-xhci \
+        -device usb-kbd \
+        -device virtio-rng-pci \
+        -blockdev node-name=pflash0,driver=file,read-only=on,filename=RISCV_VIRT_CODE.fd \
+        -blockdev node-name=pflash1,driver=file,filename=RISCV_VIRT_VARS.fd \
+        -netdev user,id=net0 \
+        -device virtio-net-pci,netdev=net0 \
+        -device virtio-blk-device,drive=hd0 \
+        -drive file=openSUSE-Tumbleweed-RISC-V-E20-efi.riscv64.raw,format=raw,id=hd0