dispatcher: documentation for parallel dispatching algorithm

src/modules/dispatcher/doc/dispatcher_admin.xml

@@ -1038,6 +1038,14 @@ end
 				distribution will be changed to 33/67/0.
 				</para>
 			</listitem>
+			<listitem>
+				<para>
+				<quote>12</quote> - dispatch to all destination in setid at
+				once (parallel forking). Note that the AVPs are no longer set
+				with the values of the destination records, no re-routing
+				making sense in this case.
+				</para>
+			</listitem>
 			<listitem>
 				<para>
 				<quote>X</quote> - if the algorithm is not implemented, the