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/ub-example.h b/ub-example.h
new file mode 100644
index 0000000..131c807
--- /dev/null
+++ b/ub-example.h
@@ -0,0 +1,19 @@
+/* =========================================================================
+   ub-example.h -- Example code for UsefulBuf
+
+   Copyright (c) 2022, Laurence Lundblade. All rights reserved.
+
+   SPDX-License-Identifier: BSD-3-Clause
+
+   See BSD-3-Clause license in README.md
+
+   Created on 4/8/22
+  ========================================================================== */
+#ifndef ub_example_h
+#define ub_example_h
+
+#include <stdint.h>
+
+int32_t RunUsefulBufExample(void);
+
+#endif /* ub_example_h */