security docs

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1913302 13f79535-47bb-0310-9956-ffa450edef68

SECURITY.md

@@ -1,4 +1,9 @@
 # Security
 
 If you suspect you have found a security vulnerability in Apache POI code, please read https://www.apache.org/security/
-for how to report the issue. Please do not report the details publicly until the report is reviewed.
+for how to report the issue. Please do not report the details publicly until the report is reviewed.
+
+## Secure Processing
+
+We strongly discourage users of Apache POI from using the lib to parse documents from untrusted sources. For more details,
+please read https://poi.apache.org/security.html.