docs: add guide for booting FreeBSD on qemu with rustsbi and u-boot

docs/booting-freebsd-in-qemu-using-uboot-and-rustsbi.md

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+# 使用RustSBI & U-Boot在QEMU中启动FreeBSD
+
+本教程给出了使用RustSBI和U-Boot在QEMU中启动FreeBSD的基本流程。
+
+请读者在其主机上安装必要的软件来尝试本教程的脚本。本教程是在Arch Linux上开发的。
+
+RustSBI 原型系统提供动态固件，根据前一个阶段传入的信息动态加载下一个阶段。
+
+本教程使用软件版本如下：
+
+|         软件          |  版本   |
+| :-------------------: | :-----: |
+| riscv64-linux-gnu-gcc | 14.2.0  |
+|  qemu-system-riscv64  |  9.1.1  |
+|  RustSBI Prototyper   |  0.0.0  |
+|        U-Boot         | 2024.04 |
+|       FreeBSD         |  14.1   |
+
+## 环境配置
+
+### 安装交叉编译器和QEMU
+
+For Arch Linux
+
+``` shell
+$ sudo pacman -S git riscv64-linux-gnu-gcc qemu-system-riscv
+```
+
+#### 测试是否成功安装
+
+For riscv64-linux-gnu-gcc:
+
+``` shell
+$ riscv64-linux-gnu-gcc --version
+```
+
+它将输出以下版本信息
+
+```
+riscv64-linux-gnu-gcc (GCC) 14.2.0
+Copyright (C) 2024 Free Software Foundation, Inc.
+This is free software; see the source for copying conditions.  There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+```
+
+For QEMU:
+
+``` shell
+$ qemu-system-riscv64 --version
+```
+
+它将输出以下版本信息
+
+```
+QEMU emulator version 9.1.1
+Copyright (c) 2003-2024 Fabrice Bellard and the QEMU Project developers
+```
+
+### 准备RustSBI Prototyper， U-Boot和FreeBSD镜像
+
+创建工作目录并进入该目录
+
+``` shell
+$ mkdir workshop && cd workshop
+```
+
+Clone RustSBI Prototyper
+
+``` shell
+$ git clone https://github.com/rustsbi/prototyper.git && cd prototyper && git checkout main && cd ..
+```
+
+Clone U-Boot
+
+``` shell
+$ git clone https://github.com/u-boot/u-boot.git && cd u-boot && git checkout v2024.04 && cd ..
+```
+
+Download FreeBSD
+``` shell
+$ wget https://download.freebsd.org/releases/VM-IMAGES/14.1-RELEASE/riscv64/Latest/FreeBSD-14.1-RELEASE-riscv-riscv64.raw.xz && xz -d FreeBSD-14.1-RELEASE-riscv-riscv64.raw.xz
+```
+
+
+## 编译RustSBI  Prototyper
+
+进入prototyper目录
+
+``` shell
+$ cd prototyper
+```
+
+编译RustSBI  Prototyper
+
+``` shell
+$ cargo make prototyper
+```
+
+## 编译U-Boot SPL
+
+进入U-Boot目录
+
+``` shell
+$ cd u-boot
+```
+
+导出环境变量
+
+``` shell
+$ export ARCH=riscv
+$ export CROSS_COMPILE=riscv64-linux-gnu-
+$ export OPENSBI=../prototyper/target/riscv64imac-unknown-none-elf/release/rustsbi-prototyper.bin
+```
+
+生成`.config`文件
+
+``` shell
+# To generate .config file out of board configuration file
+$ make qemu-riscv64_spl_defconfig
+```
+
+编译U-Boot
+
+``` shell
+# To build U-Boot
+$ make -j$(nproc)
+```
+
+本小节将使用二进制文件 `./spl/u-boot-spl`和`./u-boot.itb `。
+
+## 使用RustSBI 原型系统和U-Boot启动Linux Kernel
+
+进入`workshop`目录
+
+``` shell
+$ cd workshop
+```
+
+运行下面命令
+
+``` shell
+$ qemu-system-riscv64 -M virt -smp 1 -m 256M -nographic \
+          -bios ./u-boot/spl/u-boot-spl \
+          -device loader,file=./u-boot/u-boot.itb,addr=0x80200000 \
+          -blockdev driver=file,filename=./FreeBSD-14.1-RELEASE-riscv-riscv64.raw,node-name=hd0 \
+          -device virtio-blk-device,drive=hd0
+```