Return HTML from a Drupal 8 form

 'textfield',
    '#title' => 'Search it',
    '#size' => 40,
    '#maxlength' => 60,
    );
    if (!empty($form_state->get('mymarkup'))) {
      $form['mymarkup'] = array(
        '#markup' => 'there we are shalom from me to you',
      );
     }
    $form['submit'] = array(
      '#type' => 'submit',
      '#value' => t('Search'),
    );
    if ($form_state->getValue('user_search')) {
        dpm("form submitted");
    }
    dpm($form);
    // drupal_set_message("
" . print_r($form_state, TRUE) . "
");

    return $form;

  }

  /**

   * {@inheritdoc}

   */

  public function validateForm(array &$form, FormStateInterface $form_state) {

    // Validate the form values.
  }
  /**

   * {@inheritdoc}

   */

  public function submitForm(array &$form, FormStateInterface $form_state) {

    dpm($form_state->getValue('user_search'));

    $form_state->set('mymarkup', 'Your search has been completed');

    $form_state->setRebuild(TRUE);

  }
}