Users: clarify the docs for WP_User::__set to make it clear that it does save data in the database.

Props johnpbloch.
Fixes #24255.


git-svn-id: https://develop.svn.wordpress.org/trunk@34379 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-user.php

@@ -305,6 +305,9 @@ class WP_User {
 	/**
 	 * Magic method for setting custom user fields.
 	 *
+	 * This method does not update custom fields in the database. It only stores
+	 * the value on the WP_User instance.
+	 *
 	 * @since 3.3.0
 	 * @access public
 	 *