Update docs

docs/clients-zh.md

@@ -238,6 +238,8 @@ Fedora 28（和更新版本）和 CentOS 8/7 用户可以使用 [IPsec/XAuth](cl
 
 > 错误 809：无法建立计算机与 VPN 服务器之间的网络连接，因为远程服务器未响应。这可能是因为未将计算机与远程服务器之间的某种网络设备(如防火墙、NAT、路由器等)配置为允许 VPN 连接。请与管理员或服务提供商联系以确定哪种设备可能产生此问题。
 
+**注：** 仅当你使用 IPsec/L2TP 模式连接到 VPN 时，才需要进行下面的注册表更改。对于 [IKEv2](ikev2-howto-zh.md) 和 [IPsec/XAuth](clients-xauth-zh.md) 模式，无需进行此更改。
+
 要解决此错误，在首次连接之前需要<a href="https://documentation.meraki.com/MX-Z/Client_VPN/Troubleshooting_Client_VPN#Windows_Error_809" target="_blank">修改一次注册表</a>，以解决 VPN 服务器 和/或 客户端与 NAT （比如家用路由器）的兼容问题。请下载并导入下面的 `.reg` 文件，或者打开 <a href="http://www.cnblogs.com/xxcanghai/p/4610054.html" target="_blank">提升权限命令提示符</a> 并运行以下命令。**完成后必须重启计算机。**
 
 - 适用于 Windows Vista, 7, 8.x 和 10 ([下载 .reg 文件](https://dl.ls20.com/reg-files/v1/Fix_VPN_Error_809_Windows_Vista_7_8_10_Reboot_Required.reg))

docs/clients.md

@@ -237,6 +237,8 @@ First check <a href="https://github.com/nm-l2tp/NetworkManager-l2tp/wiki/Prebuil
 
 > Error 809: The network connection between your computer and the VPN server could not be established because the remote server is not responding. This could be because one of the network devices (e.g, firewalls, NAT, routers, etc) between your computer and the remote server is not configured to allow VPN connections. Please contact your Administrator or your service provider to determine which device may be causing the problem.
 
+**Note:** The registry change below is only required if you use IPsec/L2TP mode to connect to the VPN. It is NOT required for the [IKEv2](ikev2-howto.md) and [IPsec/XAuth](clients-xauth.md) modes.
+
 To fix this error, a <a href="https://documentation.meraki.com/MX-Z/Client_VPN/Troubleshooting_Client_VPN#Windows_Error_809" target="_blank">one-time registry change</a> is required because the VPN server and/or client is behind NAT (e.g. home router). Download and import the `.reg` file below, or run the following from an <a href="http://www.winhelponline.com/blog/open-elevated-command-prompt-windows/" target="_blank">elevated command prompt</a>. **You must reboot your PC when finished.**
 
 - For Windows Vista, 7, 8.x and 10 ([download .reg file](https://dl.ls20.com/reg-files/v1/Fix_VPN_Error_809_Windows_Vista_7_8_10_Reboot_Required.reg))