docs: 更新 Snow-Lang 语法规范文档链接

- 移除了文档链接末尾的 ".md" 后缀
- 统一文档链接格式，与其他文档链接保持一致

README.md

@@ -71,7 +71,7 @@ Snow 语言受到 LLM 驱动代码生成趋势的启发,强调简单而清晰的
 ## 相关文档
 [Snow-Lang 指南](docs/Snow-Lang-Syntax/Snow-Lang-Syntax.md)
 
-[Snow-Lang 语法规范](docs/Snow-Lang-Syntax/Snow-Lang-Grammar-Specification.md)
+[Snow-Lang 语法规范](docs/Snow-Lang-Syntax/Snow-Lang-Grammar-Specification)
 
 
 [Git 管理规范](docs/Snow-Lang-Git-Management/Snow-Lang-Git-Management.md)