Adding notice about usage of the data format header in the unit test

The original header definition has served as basis for the discussion,
the final definition has been developed elsewhere and is soon to be
merged. The very early definition is temporarily kept for the unit test.

Author: matthiasrichter

DataFormats/Generic/test/memory-format.h

@@ -12,10 +12,14 @@
 //* any purpose. It is provided "as is" without express or implied warranty. *
 //****************************************************************************
 
-//  @file   memory_format.h
-//  @author Matthias Richter
-//  @since  2016-01-28
-//  @brief  Primitives for the ALICE O2 in-memory format
+/// @file   memory_format.h
+/// @author Matthias Richter
+/// @since  2016-01-28
+/// @brief  Helper structs for the ALICE O2 generic format API test
+/// @note   DO NOT USE OUTSIDE UNIT TEST OF FORMAT API
+///         This definitions have been a first draft during discussion of
+///         in memory data formats, the final header file has been placed
+///         elsewhere, but this file is temporarily kept for the unit test
 
 // use the standard definitions of int variables
 #include <stdint.h>