add trademark declarations

Signed-off-by: NCaspar Zhang <caspar@linux.alibaba.com>

README.md

@@ -100,3 +100,7 @@ We use the same license as the upstream does, so please refer to the [COPYING](C
 + Join the [mailing list discussions](MAILLIST.md);
 + Join the [forum discussions](https://bbs.aliyun.com/thread/450.html);
 + Send us an E-mail to [alicloud-linux-os@service.alibaba.com](mailto:alicloud-linux-os@service.alibaba.com) is always a good idea.
+
+--------------------------------
+
+> The registered trademark Linux® is used pursuant to a sublicense from the Linux Foundation, the exclusive licensee of Linus Torvalds, owner of the mark on a world­wide basis.

os.md

@@ -46,3 +46,7 @@ To get helps when using Alibaba Cloud Linux OS, you can
 + Join the [mailing list discussions](MAILLIST.md);
 + Join the [forum discussions](https://bbs.aliyun.com/thread/450.html);
 + Send us an E-mail to [alicloud-linux-os@service.alibaba.com](mailto:alicloud-linux-os@service.alibaba.com).
+
+------------------------
+
+> The registered trademark Linux® is used pursuant to a sublicense from the Linux Foundation, the exclusive licensee of Linus Torvalds, owner of the mark on a world­wide basis.

zh/README.md

@@ -103,3 +103,7 @@ ALK 和 Alibaba Cloud Linux OS 项目是“站在巨人的肩膀上”且聚合
 + 加入[邮件列表](MAILLIST.md)参与讨论；
 + 加入[开发者论坛](https://bbs.aliyun.com/thread/450.html)参与讨论；
 + 或者可以给我们发邮件：[alicloud-linux-os@service.alibaba.com](mailto:alicloud-linux-os@service.alibaba.com).
+
+--------------------------------
+
+> The registered trademark Linux® is used pursuant to a sublicense from the Linux Foundation, the exclusive licensee of Linus Torvalds, owner of the mark on a world­wide basis.

zh/os.md

@@ -47,3 +47,7 @@ sudo yumdownloader --source <包名>
 + 可以加入[开发者论坛](https://bbs.aliyun.com/thread/450.html)参与讨论；
 + 可以加入钉钉群：`Alibaba Cloud Linux OS 开发者&用户群`，群号：`23149462`;
 + 或者可以给我们发邮件：[alicloud-linux-os@service.alibaba.com](mailto:alicloud-linux-os@service.alibaba.com).
+
+--------------------------------
+
+> The registered trademark Linux® is used pursuant to a sublicense from the Linux Foundation, the exclusive licensee of Linus Torvalds, owner of the mark on a world­wide basis.