doc: rewritten decorator introduction

doc/examples/decorator_01.cpp

@@ -0,0 +1,25 @@
+//  (C) Copyright Andrzej Krzemienski 2015.
+//  Distributed under the Boost Software License, Version 1.0.
+//  (See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+
+//  See http://www.boost.org/libs/test for the library home page.
+
+//[example_code
+#define BOOST_TEST_MODULE decorator_01
+#include <boost/test/included/unit_test.hpp>
+namespace utf = boost::unit_test;
+
+BOOST_AUTO_TEST_CASE(test_case1, *utf::label("trivial"))
+{
+  BOOST_TEST(true);
+}
+
+BOOST_AUTO_TEST_CASE(test_case2,
+  * utf::label("trivial")
+  * utf::label("cmp")
+  * utf::description("testing equality of ones"))
+{
+  BOOST_TEST(1 == 1);
+}
+//]