Update files related to CBMC starter kit

Author: angelonakos

test/cbmc/include/README.md

@@ -0,0 +1,6 @@
+CBMC proof include files
+========================
+
+This directory contains include files written for CBMC proof.  It is
+common to write some code to model aspects of the system under test,
+and the header files for this code go here.