Add INSERT statement to example so that it can be reproduced

from John Gage

doc/src/sgml/xfunc.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/xfunc.sgml,v 1.149 2010/05/30 18:10:40 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/xfunc.sgml,v 1.150 2010/07/25 08:30:42 petere Exp $ -->
 
  <sect1 id="xfunc">
   <title>User-Defined Functions</title>
@@ -293,6 +293,8 @@ CREATE TABLE emp (
     cubicle     point
 );
 
+INSERT INTO emp VALUES ('Bill', 4200, 45, '(2,1)');
+
 CREATE FUNCTION double_salary(emp) RETURNS numeric AS $$
     SELECT $1.salary * 2 AS salary;
 $$ LANGUAGE SQL;