Add extra usage example

git-svn-id: https://plugins.svn.wordpress.org/shortcodes-to-show-or-hide-content/trunk@970238 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fix curly braces

git-svn-id: https://plugins.svn.wordpress.org/shortcodes-to-show-or-hide-content/trunk@970239 b8457f37-d9ea-0310-8a92-e5e31aec5664