update a description

git-svn-id: https://plugins.svn.wordpress.org/groupdocs-signature/trunk@791044 b8457f37-d9ea-0310-8a92-e5e31aec5664
update description

git-svn-id: https://plugins.svn.wordpress.org/groupdocs-signature/trunk@795160 b8457f37-d9ea-0310-8a92-e5e31aec5664