Bug#36998165 Add CONTRIBUTING.md and SECURITY.md files to 8.0/8.4/9

Post-push-fix: add missing newline

Change-Id: I84d101ec876c4012ef6045b56f2aaf96ada55172

Author: dahlerlend

SECURITY.md

@@ -32,4 +32,4 @@ Security-related information
 We will provide security related information such as a threat model, considerations
 for secure use, or any known security issues in our documentation. Please note
 that labs and sample code are intended to demonstrate a concept and may not be
-sufficiently hardened for production use.
+sufficiently hardened for production use.