Fix icon path for subdirectory installations

git-svn-id: https://plugins.svn.wordpress.org/smsify/trunk@961636 b8457f37-d9ea-0310-8a92-e5e31aec5664
fix path

git-svn-id: https://plugins.svn.wordpress.org/smsify/trunk@961640 b8457f37-d9ea-0310-8a92-e5e31aec5664
fix path again

git-svn-id: https://plugins.svn.wordpress.org/smsify/trunk@961643 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme

git-svn-id: https://plugins.svn.wordpress.org/smsify/trunk@961645 b8457f37-d9ea-0310-8a92-e5e31aec5664