Update readme file, add screenshots, extend description and readme

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-piwik-integration/trunk@1007919 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update readme file, add screenshots, extend description and readme

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-piwik-integration/trunk@1007924 b8457f37-d9ea-0310-8a92-e5e31aec5664