update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/svg-vector-icon-plugin/trunk@750254 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/svg-vector-icon-plugin/trunk@750255 b8457f37-d9ea-0310-8a92-e5e31aec5664