Drupal 8: Add button class to the read more link of a node

I stumbled across this solution to add attributes to the read more links of a node.

/**
 * Implements template_preprocess_links()
 */
function MYTHEME_preprocess_links(&$variables) {
  $variables['links']['node-readmore']['link']['#options']['attributes']['class'][] = 'button';
  $variables['links']['comment-add']['link']['#options']['attributes']['class'][] = 'button';
}

Thanks: http://drupal.stackexchange.com/a/186323