added hook_help

Closes #3372515

library_generator.module

 <?php
 
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Url;
+
 /**
  * @file
  * The library_generator module file.
@@ -12,3 +15,27 @@ function library_generator_library_info_alter(&$libraries, $extension) {
   $generated_libraries = \Drupal::service('library_generator.discovery')->getLibrariesByExtension($extension);
   $libraries = array_merge($generated_libraries, $libraries);
 }
+
+/**
+ * Implements hook_help().
+ */
+function library_generator_help($route_name, RouteMatchInterface $route_match)
+{
+  switch ($route_name) {
+    case 'help.page.library_generator':
+      $output = '';
+      $output .= '<h3>' . t('About') . '</h3>';
+      $output .= '<p>' . t(
+        'The Library Generator module generates asset libraries for CSS and JS files in modules and themes, see the <a href=":handbook">
+      online documentation for the Custom Account Link module</a>.',
+        [
+          ':library_generator' => Url::fromRoute('help.page', ['name' => 'library_generator'])->toString(),
+          ':handbook' => 'https://www.drupal.org/project/library_generator'
+        ]
+      ) . '</p>';
+      $output .= '<h3>' . t('Uses') . '</h3>';
+      $output .= '<p>' . t(' This module is used when you want a separate asset library for each CSS and JS file without having to add them manually to your *.libraries.yml');
+      $output .= '</p>';
+      return $output;
+  }
+}
\ No newline at end of file