README: Added note about IAM roles
README: Added note about IAM roles

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