update sphinx index option description

config.php-dist

@@ -114,9 +114,10 @@
 	define('SPHINX_SERVER', 'localhost:9312');
 	// Hostname:port combination for the Sphinx server.
 
-	define('SPHINX_INDEX', 'ttrss');
+	define('SPHINX_INDEX', 'ttrss, delta');
 	// Index name in Sphinx configuration. You can specify multiple indexes
 	// as a comma-separated string.
+	// Example configuration files are available on tt-rss wiki.
 
 	// ***********************************
 	// *** Self-registrations by users ***