message: operator |= for expected::Result
diff: @@ -338,6 +338,12 @@ namespace iroha {
  [](auto &&e) { return return_type(makeError(std::move(e.error))); });
  }
  + /// operator |= is a shortcut for `Result = Result | function'
  + template <typename R, typename F>
  + constexpr auto operator|=(R &r, F &&f) -> decltype(r = r | f) {
  + return r = r | std::forward<F>(f);
  + }
  +
  /**
  * Polymorphic Result is simple alias for result type, which can be used to
  * work with polymorphic objects. It is achieved by wrapping V and E in a
  