Add issue template (#341)

Author: alex-chew

.github/ISSUE_TEMPLATE/aws-encryption-sdk-issue.md

@@ -0,0 +1,26 @@
+---
+name: AWS Encryption SDK Issue
+about: AWS Encryption SDK Issue
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+### Security issue notifications
+
+If you discover a potential security issue in the AWS Encryption SDK we ask that you notify AWS Security via our [vulnerability reporting page](https://aws.amazon.com/security/vulnerability-reporting/). Please do **not** create a public GitHub issue.
+
+### Problem:
+
+A short description of what the problem is and why we need to fix it. Add reproduction steps if necessary.
+
+### Solution:
+
+A description of the possible solution in terms of Encryption SDK architecture.
+
+### Out of scope:
+
+Is there anything the solution will intentionally NOT address?
+
+[//]: #  (NOTE: If you believe this might be a security issue, please email [email protected] instead of creating a GitHub issue. For more details, see the AWS Vulnerability Reporting Guide: https://aws.amazon.com/security/vulnerability-reporting/ )