To install the ArticleToCategory2 extension, put the following line in LocalSettings.php:

require_once( "$IP/extensions/ArticleToCategory2/ArticleToCategory2.php" );
$wgarticletocategory2ConfigBlacklist=false;
$wgGroupPermissions['*']['ArticleToCategory2'] = true;
$wgGroupPermissions['*']['ArticleToCategory2AddCat'] = false;