[BSP] Add README.md in x86

bsp/x86/README.md

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+# RT-Thread for x86
+
+这是一份基础的RT-Thread针对x86的版本、移植，主要是能够在qemu中执行。以下说明主要针对Linux的环境，如果是Windows环境，请使用Env工具，同时请自行处理生成iso的方法。
+
+## 编译
+
+编译RT-Thread for x86版本，还需要一份支持newlib的工具链，可以通过以下地址获得：
+
+*[i386-unknown-elf_for_x86_64-pc-linux-gnu_latest.tar.bz2](http://117.143.63.254:9012/www/rt-smart/i386-unknown-elf_for_x86_64-pc-linux-gnu_latest.tar.bz2)
+
+下载后解压，然后在rtconfig.py中配置其中的EXEC_PATH变量
+
+```python
+if  CROSS_TOOL == 'gcc':
+    PLATFORM    = 'gcc'
+    EXEC_PATH   = os.getenv('RTT_EXEC_PATH') or 'E:/Program Files/CodeSourcery/Sourcery_CodeBench_Lite_for_IA32_ELF/bin'
+
+```
+
+然后在x86 bsp目录下执行scons命令来编译：
+
+```bash
+scons
+```
+
+### 配置
+
+RT-Thread for x86的版本也支持menuconfig的配置方式，在Linux下可以使用`scons --menuconfig`的方式进行配置。
+
+因为menuconfig是一份字符界面的配置（Kconfig），在ubuntu下需要安装ncurses5的库
+
+```bash
+sudo apt install libncurses5-dev
+```
+
+## 运行
+
+在ubuntu下运行，请确保你安装了`qemu-system-i386`，`grub` 以及 `xorriso`软件包：
+
+```bash
+sudo apt install qemu-system-x86 grub-common xorriso
+```
+
+然后执行`./run.sh`命令可以使用qemu来模拟执行(它也会生成可启动的iso文件)
+
+```bash
+~/workspace/rt-thread/bsp/x86$ ./run.sh
+xorriso 1.4.8 : RockRidge filesystem manipulator, libburnia project.
+
+Drive current: -outdev 'stdio:bootable.iso'
+Media current: stdio file, overwriteable
+Media status : is blank
+Media summary: 0 sessions, 0 data blocks, 0 data,  135g free
+Added to ISO image: directory '/'='/tmp/grub.uLz91i'
+xorriso : UPDATE : 578 files added in 1 seconds
+Added to ISO image: directory '/'='/home/bernard/workspace/rt-thread/bsp/x86/root'
+xorriso : UPDATE : 582 files added in 1 seconds
+xorriso : NOTE : Copying to System Area: 512 bytes from file '/usr/lib/grub/i386-pc/boot_hybrid.img'
+ISO image produced: 6007 sectors
+Written to medium : 6007 sectors at LBA 0
+Writing to 'stdio:bootable.iso' completed successfully.
+
+
+ \ | /
+- RT -     Thread Operating System
+ / | \     4.0.4 build Aug 22 2021
+ 2006 - 2021 Copyright by rt-thread team
+Floppy Inc : NEC765B controller  Floppy Type : 2.88MB
+hello!
+msh />
+```
+
+在qemu下可以按Ctrl-A + X退出qemu。