Updated readme to show example with checking for WP error

git-svn-id: https://plugins.svn.wordpress.org/fb-last-posts/trunk@989945 b8457f37-d9ea-0310-8a92-e5e31aec5664
Tagging version 1.0.1

git-svn-id: https://plugins.svn.wordpress.org/fb-last-posts/trunk@989947 b8457f37-d9ea-0310-8a92-e5e31aec5664