List: refactor documentation

example/list/nil.cpp

@@ -0,0 +1,16 @@
+/*
+@copyright Louis Dionne 2014
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+ */
+
+#include <boost/hana/detail/static_assert.hpp>
+#include <boost/hana/list/instance.hpp>
+using namespace boost::hana;
+
+
+int main() {
+    //! [main]
+    BOOST_HANA_STATIC_ASSERT(nil<List> == list());
+    //! [main]
+}