Update docs

- Re-add DigitalOcean deploy button.
  Ref: carlfriess/DigitalOceanVPNSetup#11 617f981

Author: hwdsl2

README-zh.md

@@ -83,7 +83,7 @@ curl -fsSL https://git.io/vpnstart -o vpn.sh && sudo sh vpn.sh
 
 这也包括各种公共云服务中的 Linux 虚拟机，比如 [DigitalOcean](https://blog.ls20.com/digitalocean), [Vultr](https://blog.ls20.com/vultr), [Linode](https://blog.ls20.com/linode), [Microsoft Azure](https://azure.microsoft.com) 和 [OVH](https://www.ovhcloud.com/en/vps/)。[Amazon EC2](https://aws.amazon.com/ec2/) 用户可以使用 [CloudFormation](aws/README-zh.md) 或者 [用户数据](https://blog.ls20.com/ipsec-l2tp-vpn-auto-setup-for-ubuntu-12-04-on-amazon-ec2/#vpnsetup) 快速部署。
 
-[![Deploy to AWS](docs/images/aws-deploy-button.png)](aws/README-zh.md)  [![Deploy to Azure](docs/images/azure-deploy-button.png)](azure/README-zh.md)  [![Deploy to Linode](docs/images/linode-deploy-button.png)](https://cloud.linode.com/stackscripts/37239)
+[![Deploy to DigitalOcean](docs/images/do-install-button.png)](http://dovpn.carlfriess.com)  [![Deploy to Linode](docs/images/linode-deploy-button.png)](https://cloud.linode.com/stackscripts/37239)  [![Deploy to AWS](docs/images/aws-deploy-button.png)](aws/README-zh.md)  [![Deploy to Azure](docs/images/azure-deploy-button.png)](azure/README-zh.md)
 
 [**» 我想建立并使用自己的 VPN ，但是没有可用的服务器**](https://blog.ls20.com/ipsec-l2tp-vpn-auto-setup-for-ubuntu-12-04-on-amazon-ec2/#gettingavps)
 

README.md

@@ -83,7 +83,7 @@ A dedicated server or virtual private server (VPS), freshly installed with one o
 
 This also includes Linux VMs in public clouds, such as [DigitalOcean](https://blog.ls20.com/digitalocean), [Vultr](https://blog.ls20.com/vultr), [Linode](https://blog.ls20.com/linode), [Microsoft Azure](https://azure.microsoft.com) and [OVH](https://www.ovhcloud.com/en/vps/). [Amazon EC2](https://aws.amazon.com/ec2/) users can deploy rapidly using [CloudFormation](aws/README.md) or [user data](https://blog.ls20.com/ipsec-l2tp-vpn-auto-setup-for-ubuntu-12-04-on-amazon-ec2/#vpnsetup).
 
-[![Deploy to AWS](docs/images/aws-deploy-button.png)](aws/README.md)  [![Deploy to Azure](docs/images/azure-deploy-button.png)](azure/README.md)  [![Deploy to Linode](docs/images/linode-deploy-button.png)](https://cloud.linode.com/stackscripts/37239)
+[![Deploy to DigitalOcean](docs/images/do-install-button.png)](http://dovpn.carlfriess.com)  [![Deploy to Linode](docs/images/linode-deploy-button.png)](https://cloud.linode.com/stackscripts/37239)  [![Deploy to AWS](docs/images/aws-deploy-button.png)](aws/README.md)  [![Deploy to Azure](docs/images/azure-deploy-button.png)](azure/README.md)
 
 [**» I want to run my own VPN but don't have a server for that**](https://blog.ls20.com/ipsec-l2tp-vpn-auto-setup-for-ubuntu-12-04-on-amazon-ec2/#gettingavps)