title: use Carbon Fields in custom plugin class
body: <p>I have a plugin which has no functionality so far. This is the current structure:</p>
  
  <pre><code>&lt;?php
  class Test
  {
      public function __construct()
      {
  
      }
  }
  
  $wpTest = new Test();
  </code></pre>
  
  <p>I want to use the <a href="https://carbonfields.net/" rel="nofollow noreferrer">Carbon Fields</a> WordPress plugin. After installing it I changed the structure according to the instructions from the website, only with the adaptation to OOP.</p>
  
  <pre><code>&lt;?php
  use Carbon_Fields\Container;
  use Carbon_Fields\Field;
  
  class Test
  {
  
      public function __construct()
      {
          add_action( 'carbon_fields_register_fields', array( $this, 'crb_attach_theme_options') );
          add_action( 'after_setup_theme', array( $this , 'crb_load' ) );
      }
  
      public function crb_load()
      {
          require_once( 'vendor/autoload.php' );
          \Carbon_Fields\Carbon_Fields::boot();
      }
  
      public function crb_attach_theme_options()
      {
          Container::make( 'theme_options', __( 'Plugin Options', 'crb' ) )
              -&gt;add_fields( array(
                  Field::make( 'text', 'crb_text', 'Text Field' ),
              ) );
      }
  
  }
  
  $wpTest = new Test();
  </code></pre>
  
  <p>It does not work. How do I fix it?</p>