Make Archives.php Include Custom Post Types. Source: https://css-tricks.com/snippets/wordpress/make-archives-php-include-custom-post-types/
<?php
function namespace_add_custom_types( $query ) {
if( is_category() || is_tag() && empty( $query->query_vars['suppress_filters'] ) ) {
$query->set( 'post_type', array(
'post', 'nav_menu_item', 'your-custom-post-type-here'
));
return $query;
}
}
add_filter( 'pre_get_posts', 'namespace_add_custom_types' );