Document the AllowSingleHopExits option

doc/tor.1.txt

@@ -751,6 +751,11 @@ The following options are useful only for clients (that is, if
     Like WarnPlaintextPorts, but instead of warning about risky port uses, Tor
     will instead refuse to make the connection. (Default: None).
 
+**AllowSingleHopCircuits** **0**|**1**::
+    When this option is set, the attached Tor controller Tor can use relays
+    that have the **AllowSingleHopExits** option turned on to build
+    one-hop Tor connections.
+
 SERVER OPTIONS
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