style: add TODO comment for when to update

src/include/units/bits/external/type_traits.h

@@ -74,6 +74,7 @@ void to_base_specialization_of(const volatile Type<Params...>*);
 }  // namespace detail
 
 template<typename T, template<typename...> typename Type>
+// inline constexpr bool // TODO: Replace with concept when it works with MSVC
 concept is_derived_from_specialization_of = requires { detail::to_base_specialization_of<Type>(std::declval<const volatile T*>()); };
 
 }  // namespace units