update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/alipay-for-woocommerce/trunk@793356 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/alipay-for-woocommerce/trunk@793359 b8457f37-d9ea-0310-8a92-e5e31aec5664