Update docs

- Add Windows PowerShell commands for creating a VPN connection
- Closes #478. Thanks @nzbart!

docs/clients-zh.md

@@ -48,6 +48,15 @@
 1. 单击 **确定** 关闭 **高级设置**。
 1. 单击 **确定** 保存 VPN 连接的详细信息。
 
+另外，除了按照以上步骤操作，你也可以运行下面的 Windows PowerShell 命令来创建 VPN 连接。将 `你的 VPN 服务器 IP` 和 `你的 VPN IPsec PSK` 换成你自己的值，用单引号括起来：
+
+```console
+# 不保存命令行历史记录
+Set-PSReadlineOption –HistorySaveStyle SaveNothing
+# 创建 VPN 连接
+Add-VpnConnection -Name 'My IPsec VPN' -ServerAddress '你的 VPN 服务器 IP' -TunnelType L2tp -EncryptionLevel Required -AuthenticationMethod Chap,MSChapv2 -L2tpPsk '你的 VPN IPsec PSK' -Force -RememberCredential -PassThru
+```
+
 **注：** 在首次连接之前需要修改一次注册表。请参见下面的说明。
 
 ### Windows 7, Vista and XP

docs/clients.md

@@ -48,6 +48,15 @@ After <a href="https://github.com/hwdsl2/setup-ipsec-vpn" target="_blank">settin
 1. Click **OK** to close the **Advanced settings**.
 1. Click **OK** to save the VPN connection details.
 
+Alternatively, instead of following the steps above, you may create the VPN connection using these Windows PowerShell commands. Replace `Your VPN Server IP` and `Your VPN IPsec PSK` with your own values, enclosed in single quotes:
+
+```console
+# Disable persistent command history
+Set-PSReadlineOption –HistorySaveStyle SaveNothing
+# Create VPN connection
+Add-VpnConnection -Name 'My IPsec VPN' -ServerAddress 'Your VPN Server IP' -TunnelType L2tp -EncryptionLevel Required -AuthenticationMethod Chap,MSChapv2 -L2tpPsk 'Your VPN IPsec PSK' -Force -RememberCredential -PassThru
+```
+
 **Note:** A one-time registry change is required before connecting. See details below.
 
 ### Windows 7, Vista and XP