doc: specify kernel requirement for trace command

docs/en/README.md

@@ -27,6 +27,10 @@ This feature requires kernel version of the machine >= 5.8.
 
 Note that if you bind dae to WAN only, dae only provide network service for local programs and not impact traffic coming in from other interfaces.
 
+`Use trace command`
+
+If you want to use `dae trace` command to triage network connectivity issue, the kernel version is required to be >= 5.15.
+
 ## Kernel Configurations
 
 Usually, mainstream desktop distributions have these items turned on. But in order to reduce kernel size, some items are turned off by default on embedded device distributions like OpenWRT, Armbian, etc.

docs/zh/README.md

@@ -25,6 +25,10 @@
 
 如果你只在 `wan_interface` 中填写了接口或 `auto`，而未在 `lan_interface` 中填写内容，那么从局域网中传来的流量将无法被代理。如果你想同时代理本机和局域网流量，请同时填写 `wan_interface` 和 `lan_interface`。
 
+`使用 trace 命令`
+
+如果你想用 `dae trace` 命令来诊断网络连通性问题，所在的设备内核版本要求 >= 5.15 。
+
 ## 内核配置选项
 
 通常，主流桌面发行版都会打开这些选项。但是为了减小内核大小，在嵌入式设备发行版（如 OpenWRT、Armbian 等）上这些选项可能处于关闭状态。使用以下命令在你的设备上显示内核配置选项：