fix: modified readme document

boot/readme.md

@@ -1,6 +1,6 @@
 1. `boot.inc` 文件放置在 `include` 目录下，所以编译的时候需要添加 `-I` 参数
 
-    ```language=sh
+    ```sh
        boot git:(master) ✗ nasm -I include/ -o mbr.bin mbr.s
        boot git:(master) ✗ nasm -I include/ -o loader.bin loader.S
     ```