update description in readme file

git-svn-id: https://plugins.svn.wordpress.org/tidio-live-chat/trunk@937965 b8457f37-d9ea-0310-8a92-e5e31aec5664
update description

git-svn-id: https://plugins.svn.wordpress.org/tidio-live-chat/trunk@937967 b8457f37-d9ea-0310-8a92-e5e31aec5664