Headless installation (#390)

Fixes #261

README.md

@@ -37,6 +37,27 @@ In your home directory, you will have `.ovpn` files. These are the client config
 
 If you have any question, head to the [FAQ](#faq) first.
 
+### Headless install
+
+It's also possible to run the script headless, e.g. without waiting for user input, in an automated manner.
+
+Example usage:
+```bash
+export APPROVE_INSTALL=y
+export APPROVE_IP=y
+export IPV6_SUPPORT=n
+export PORT_CHOICE=1
+export PROTOCOL_CHOICE=1
+export DNS=1
+export COMPRESSION_ENABLED=n
+export CUSTOMIZE_ENC=n
+export CLIENT=clientname
+export PASS=1
+./openvpn-install.sh
+```
+
+If the server is behind NAT, you can specify its endpoint with the `PUBLICIP` variable. It the endpoint is the public IP address which it is behind, you can use `export PUBLICIP=$(curl ifconfig.co)`.
+
 ## Features
 
 - Installs and configures a ready-to-use OpenVPN server