Add UsefulBuf example code (#136)

* fix grammer in security policy

* first check-in of UsefulBuf example

* Code tidy, comment wording, spelling...

Co-authored-by: Laurence Lundblade <lgl@securitytheory.com>
diff --git a/cmd_line_main.c b/cmd_line_main.c
index ef59e43..59ceb3a 100644
--- a/cmd_line_main.c
+++ b/cmd_line_main.c
@@ -13,6 +13,7 @@
 #include <stdio.h>
 #include "run_tests.h"
 #include "example.h"
+#include "ub-example.h"
 
 
 /*
@@ -33,6 +34,7 @@
    (void)argc; // Avoid unused parameter error
 
    RunQCborExample();
+   RunUsefulBufExample();
 
 
    // This call prints out sizes of data structures to remind us