Update README.md

Author: quantumiracle

README.md

@@ -124,7 +124,9 @@ Since Tensorflow 2.0 has already incorporated the dynamic graph construction ins
 ](https://arxiv.org/abs/2011.07553)
 
  * **Probabilistic Mixture-of-Experts (PMOE)** :
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    PMOE uses a differentiable multi-modal Gaussian distribution to replace the standard unimodal Gaussian distribution for policy representation.
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    `pmoe_sac.py`: based on off-policy SAC.
 
    `pmoe_ppo.py`: based on on-policy PPO.