Update readme with security notification blurb (#295)

Author: bryan-aguilar

README.md

@@ -39,3 +39,6 @@ used as is.
 ## Support
 
 Please note that as per policy, we're providing support via GitHub on a best effort basis. However, if you have AWS Enterprise Support you can create a ticket and we will provide direct support within the respective SLAs.
+
+## Security issue notifications
+If you discover a potential security issue in this project we ask that you notify AWS/Amazon Security via our [vulnerability reporting page](http://aws.amazon.com/security/vulnerability-reporting/). Please do **not** create a public github issue.