Try to improve documentation for DirAuthority's port field.

Closes ticket 20152

changes/doc20152

@@ -0,0 +1,3 @@
+  o Documentation:
+    - Improve the documentation for the directory port part of the
+      DirAuthority line. Closes ticket 20152.

doc/tor.1.txt

@@ -436,9 +436,11 @@ GENERAL OPTIONS
     authority is listening for IPv6 connections on the indicated IPv6 address
     and OR Port. +
  +
-    Tor will contact the authority at __address__:__port__ (the DirPort) to
-    download directory documents. If an IPv6 address is supplied, Tor will
-    also download directory documents at the IPv6 address on the DirPort. +
+    Tor will contact the authority at __address__ to
+    download directory documents. The provided __port__ value is a dirport;
+    clients ignore this in favor of the specified "orport=" value.  If an
+    IPv6 address is supplied, Tor will
+    also download directory documents at the IPv6 address on the ORPort. +
  +
     If no **DirAuthority** line is given, Tor will use the default directory
     authorities. NOTE: this option is intended for setting up a private Tor