Update CHANGELOG.md with Discovery feature hardening improvements

Author: Bob Strahan

CHANGELOG.md

@@ -35,6 +35,7 @@ SPDX-License-Identifier: MIT-0
 - Fix occasional UI error 'Failed to get document details - please try again later' - resolves #58
 - Fixed UI zipfile creation to exclude .aws-sam directories and .env files from deployment package
 - Added security recommendation to set LogLevel parameter to WARN or ERROR (not INFO) for production deployments to prevent logging of sensitive information including PII data, document contents, and S3 presigned URLs
+- Hardened several aspects of the new Discovery feature
 
 ## [0.3.15]