message: [tf.data] Add some comment for recent change.
diff: @@ -77,6 +77,13 @@ struct Parameter {
  Parameter(const string& name, std::shared_ptr<SharedState> state, double min,
  double max)
  : name(name),
  + // Sometimes non-autotune nodes (with `autotune_=false`) may contain
  + // parameters (for example inputs of parallel interleave dataset which
  + // are not in the current cycle). To avoid unrealistic situation
  + // (say `buffer_size=-1` or `parallelism=-1`) in the optimization
  + // computation, if the state value is `kAutotune=-1` (just to indicate
  + // the `SharedState` is tunable), we initialize the parameter value to
  + // be the minimal value of the state.
  value(state->value == kAutotune ? min : state->value),
  min(min),
  max(max),
  