Add documentation for PERSIST_TUN_ACTION (Android specific)

index 871e399..466afba 100644
@@ -2,7 +2,7 @@ This file documents the support in OpenVPN for Android 4.0 and up.
 
 This support is primarily used in the "OpenVPN for Android" app
 (http://code.google.com/p/ics-openvpn/). For building see the developer
-README: http://code.google.com/p/ics-openvpn/source/browse/README.txt.
+README: http://code.google.com/p/ics-openvpn/source/browse/doc/README.txt.
 
 Android provides the VPNService API
 (http://developer.android.com/reference/android/net/VpnService.html)

@@ -55,6 +55,21 @@ To set the DNS server and search domain.
 The GUI will then respond with a "needok 'command' ok' or "needok
 'command' cancel', e.g. "needok 'IFCONFIG' ok".
 
+PERSIST_TUN_ACTION
+
+In Android 4.4-4.4.2 a bug exists that does not allow to open a new tun fd
+while a tun fd is still open. When OpenVPN wants to open an fd it will do
+this query. The UI should compare the last configuration of 
+the tun device with the current tun configuration and reply with either (or
+always respond with OPEN_AFTER_BEFORE/OPEN_BEFORE_CLOSE)
+
+- NOACTION: Keep using the old fd
+- OPEN_AFTER_CLOSE: First close the old fd and then open a new to workaround the bug
+- OPEN_BEFORE_CLOSE: the normal behaviour when the VPN configuration changed
+
+For example the UI could respond with 
+needok 'PERSIST_TUN_ACTION' OPEN_AFTER_CLOSE
+
 To protect a socket the OpenVPN will send a PROTECTFD to the UI.
 When sending the PROTECTFD command command to the UI it will send
 the fd of the socket as ancillary message over the UNIX socket.

@@ -74,3 +89,4 @@ are not specific to Android but are rarely used on other platform.
 For example using SIGUSR1 and management-hold to restart, pause,
 continue the VPN on network changes or the external key management
 --management-external-key option and inline files.
+