added hook help

node_access_grants.module

@@ -2,6 +2,7 @@
 
 use Drupal\Core\Session\AccountInterface;
 use Drupal\node\NodeInterface;
+use Drupal\Core\Routing\RouteMatchInterface;
 
 /**
  * Implements hook_node_grants().
@@ -19,4 +20,20 @@ function node_access_grants_node_access_records(NodeInterface $node) {
   /** @var \Drupal\node_access_grants\NodeAccessGrantsInterface $collection */
   $collection = \Drupal::service('node_access_grants.collection');
   return $collection->accessRecords($node);
+}
+
+/**
+ * Implements hook_help().
+ */
+function node_access_grants_help($route_name, RouteMatchInterface $route_match) {
+  switch ($route_name) {
+    case 'help.page.node_access_grants':
+      $filepath = dirname(__FILE__) . '/README.md';
+      if (file_exists($filepath)) {
+        $readme = file_get_contents($filepath);
+        $output = '<pre>' . $readme . '</pre>';
+
+        return $output;
+      }
+  }
 }
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