[1.x][Docs] Added SECURITY.md (#715)

Adding SECURITY.md as it is defined in the README. Will inform developers
how to report security issues.

Issue resolved:
#714

Backport PR:
#715

Signed-off-by: Kawika Avilla <kavilla414@gmail.com>

SECURITY.md

@@ -0,0 +1,3 @@
+## Reporting a Vulnerability
+
+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/) or directly via email to aws-security@amazon.com. Please do **not** create a public GitHub issue.