How to define fcnet_hiddens size and number of layers in rllib tune?

@sirjay I still try to combine rllib algorithm with objective function. I hope the examples below can help me somehow:
https://github.com/ray-project/ray/blob/master/rllib/examples/custom_experiment.py
https://docs.ray.io/en/latest/tune/api_docs/trainable.html#training-tune-trainable-tune-report