Docs: Document the globals used in some REST API methods.

See #53399.

git-svn-id: https://develop.svn.wordpress.org/trunk@51278 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php

@@ -1173,6 +1173,8 @@ class WP_REST_Users_Controller extends WP_REST_Controller {
 	 *
 	 * @since 4.7.0
 	 *
+	 * @global WP_Roles $wp_roles WordPress role management object.
+	 *
 	 * @param int   $user_id User ID.
 	 * @param array $roles   New user roles.
 	 * @return true|WP_Error True if the current user is allowed to make the role change,