Issue #1858508 by TravisCarden: Add see also to hook_theme docs

core/modules/system/system.api.php

@@ -1819,6 +1819,8 @@ function hook_permission() {
  *     'module', 'theme_engine', or 'theme'.
  *   - theme path: (automatically derived) The directory path of the theme or
  *     module, so that it doesn't need to be looked up.
+ *
+ * @see hook_theme_registry_alter()
  */
 function hook_theme($existing, $type, $theme, $path) {
   return array(