title: Wordpress custom taxonomy not searchable
body: <p>Have added successfully custom taxonomy to Woo products:</p>
  
  <pre><code>$args = array(
    'labels' =&gt; array(
      'name' =&gt; 'Companies',
      'singular_name' =&gt; 'Company',
      'add_new_item' =&gt; 'Add New Company',
    ),
    'hierarchical' =&gt; true,
    'public' =&gt; true,
    'publicly_queryable' =&gt; true,
    'show_ui'=&gt; true,
    'query_var' =&gt; true,
    'exclude_from_search' =&gt; false
  );
  
  register_taxonomy( 'companies', 'product', $args );
  register_taxonomy_for_object_type( 'companies', 'product' );
  </code></pre>
  
  <p>Problem comes when I try to query this with WP search in search.php:</p>
  
  <pre><code>if(have_posts()){
    while (have_posts()) : the_post();
        echo get_the_ID();
    endwhile;
  }
  </code></pre>
  
  <p>Example: <code>/?search=My Company</code></p>
  
  <p>What's the correct approach to this? I tried to flush (update permalinks but without any success). Cannot query the Category taxonomy neither (default Woo)</p>