README: filter_opsworks_activities documentation improved
README: filter_opsworks_activities documentation improved

mixpanel-platform/chef-handler-sns,mixpanel-platform/chef-handler-sns,zuazo/chef-handler-sns,mevic/chef-handler-sns,mevic/chef-handler-sns,zuazo/chef-handler-sns,onddo/chef-handler-sns,onddo/chef-handler-sns