C++: Subsection header.

Author: geoffw0

cpp/ql/test/query-tests/Security/CWE/README.md

@@ -1,3 +1,5 @@
-# Source from the Juliet Test Suite
+# CWE specific security tests
+
+## Source from the Juliet Test Suite
 
 Some of the the files in these tests contain source code copied or derived from the public domain "Juliet Test Suite for C/C++" (provided by NIST / SAMATE Team at https://samate.nist.gov/SARD/testsuite.php).  Such tests are typically in subdirectories named "SAMATE".