Add man page entry.

doc/tor.1.txt

@@ -2835,6 +2835,11 @@ The following options are used to configure a hidden service.
    not an authorization mechanism; it is instead meant to be a mild
    inconvenience to port-scanners.) (Default: 0)
 
+[[HiddenServiceExportCircuitID]] **HiddenServiceExportCircuitID** **0**|**1**::
+   If set to 1, then the onion service will use the HAProxy proxy protocol to
+   assign a unique IPv6 address (in an unused IPv6 range) to each inbound
+   client circuit. (Default: 0)
+
 [[HiddenServiceMaxStreams]] **HiddenServiceMaxStreams** __N__::
    The maximum number of simultaneous streams (connections) per rendezvous
    circuit. The maximum value allowed is 65535. (Setting this to 0 will allow