El error te lo dice cheque el manual tenes que incluir show_news.php en tu index pero tendrias que cambiar la extensión de index.html por index.php y utilizar include.
lee el README.html
Código:
Examples
Showing Active News
<?php
include("path/to/show_news.php");
?>
Showing with Different Template
<?php
$template = "YOUR_TEMPLATE_NAME"; include("path/to/show_news.php");
?>
Showing Archives
<?php
include("path/to/show_archives.php");
?>
Showing 5 Latest News
<?php
$number = "5";
include("path/to/show_news.php");
?>
Showing 5 News from Category with ID 2
<?php
$number = "5";
$category = "2";
include("path/to/show_news.php");
?>
Showing All Headlines And The 1 Latest News Article On One Page
<?php
$static = true;
$template = "Headlines";
include("path/to/show_news.php");
$number = "1";
include("path/to/show_news.php");
?>