Docs: Add missing description for $wp_query and $wp_the_query globals.

Props mukesh27.
See #45604, #47110.

git-svn-id: https://develop.svn.wordpress.org/trunk@45739 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/export.php

@@ -525,7 +525,7 @@ function export_wp( $args = array() ) {
 	<?php
 	if ( $post_ids ) {
 		/**
-		 * @global WP_Query $wp_query
+		 * @global WP_Query $wp_query WordPress Query object.
 		 */
 		global $wp_query;