api-8.x-1.x-dev/modules/api_search_core/api_search_core.module

<?php

/**
 * @file
 * Contains api_search_core.module.
 */

use Drupal\Core\Link;
use Drupal\Core\Routing\RouteMatchInterface;

/**
 * Implements hook_help().
 */
function api_search_core_help($route_name, RouteMatchInterface $route_match) {
  $search_page_url = Link::createFromRoute(
    t('Search overview page'),
    'entity.search_page.collection'
  )->toString();
  switch ($route_name) {
    case 'help.page.api_search_core':
      $output = '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('Makes DocBlock search available in the Drupal Core Search.') . '</p>';
      $output .= '<p>' . t('Go to @search_page and see the new DocBlocks search page and endpoint.', [
        '@search_page' => $search_page_url,
      ]) . '</p>';
      return $output;

    default:
  }
}