update PolicyGradient

codes/PolicyGradient/README.md

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+# Policy Gradient
+实现的是Policy Gradient最基本的REINFORCE方法
+## 原理讲解
+
+参考我的博客[Policy Gradient算法实战](https://blog.csdn.net/JohnJim0/article/details/110236851)
+
+## 环境
+
+python 3.7.9
+
+pytorch 1.6.0
+
+tensorboard 2.3.0 
+
+torchvision 0.7.0 
+
+## 程序运行方法
+
+train: 
+
+```python
+python main.py 
+```
+
+eval: 
+
+```python
+python main.py --train 0 
+```
+tensorboard：
+```python
+tensorboard --logdir logs 
+```
+
+
+## 参考
+
+[REINFORCE和Reparameterization Trick](https://blog.csdn.net/JohnJim0/article/details/110230703)
+
+[Policy Gradient paper](https://papers.nips.cc/paper/1713-policy-gradient-methods-for-reinforcement-learning-with-function-approximation.pdf)
+
+[REINFORCE](https://towardsdatascience.com/policy-gradient-methods-104c783251e0)