adding example to pi(), mostly so that they precision is obvious

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@50236 c90b9560-bf6c-de11-be94-00142212c4b1

functions/math.xml

@@ -943,6 +943,16 @@ $randval = mt_rand();
     <simpara>
      Returns an approximation of pi.
     </simpara>
+   <para>
+    <informalexample>
+     <programlisting>
+
+echo pi();
+// echo's 3.1415926535898
+
+     </programlisting>
+    </informalexample>
+   </para>
    </refsect1>
   </refentry>