updated readme file for instruction and note

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-direct-checkout/trunk@788261 b8457f37-d9ea-0310-8a92-e5e31aec5664
updates

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-direct-checkout/trunk@788263 b8457f37-d9ea-0310-8a92-e5e31aec5664