appened custom text to content in template_preprocess_taxonomy_term drupal 8
Ok, so here is how I did it.

function cars_theme_preprocess_taxonomy_term(&amp;$variables) {
      if($variables['view_mode'] == 'full'){
         $variables['cars_view'] = "this is test";
     }
}


And then in my twig file I output the cars_view as {{ cars_view }}