Fix listing typo (#130)

The paragraph lists a couple of options and expands information on each element. However,  the following explanation lists the first element, the first, the third, and the last, whereas the logic of the discussion aims to explain the listing as first, second, third, and last elements.

Author: mrkz

doc/overview.xml

@@ -187,7 +187,7 @@ desc.add_options()
       </programlisting>
       For the first parameter, we specify only the name and the
       description. No value can be specified in the parsed source.
-      For the first option, the user must specify a value, using a single
+      For the second option, the user must specify a value, using a single
       token. For the third option, the user may either provide a single token
       for the value, or no token at all. For the last option, the value can
       span several tokens. For example, the following command line is OK: