docs: parameter expansion in pvAssign

documentation/Reference.txt

@@ -1359,7 +1359,10 @@ clause.
    Add an optional argument, so users can make pvAssign wait for the
    connection to be established (or some timeout).
 
-See also :token:`assign` clause.
+.. versionadded:: 2.2
+
+Program parameter expansion is done in the same way as
+when using the :token:`assign` clause.
 
 A better name for this function would be ``pvReassign``.