add dygraph link in readme (#559)

README.md

@@ -228,6 +228,9 @@ pip install paddleslim==1.2.0 -i https://pypi.tuna.tsinghua.edu.cn/simple
 ## 使用
 
 - [快速开始](docs/zh_cn/quick_start)：通过简单示例介绍如何快速使用PaddleSlim。
+- 动态图：
+    - 剪枝：[教程](dygraph_docs/)，[示例](demo/dygraph/pruning)
+    - 量化：[示例](demo/dygraph/quant)
 - [进阶教程](docs/zh_cn/tutorials)：PaddleSlim高阶教程。
 - [模型库](docs/zh_cn/model_zoo.md)：各个压缩策略在图像分类、目标检测和图像语义分割模型上的实验结论，包括模型精度、预测速度和可供下载的预训练模型。
 - [API文档](https://paddlepaddle.github.io/PaddleSlim/api_cn/index.html)

README_en.md

@@ -83,13 +83,25 @@ pip install paddleslim==1.2.0 -i https://pypi.tuna.tsinghua.edu.cn/simple
 ## Usage
 
 - [QuickStart](https://paddlepaddle.github.io/PaddleSlim/quick_start/index_en.html): Introduce how to use PaddleSlim by simple examples.
+- Dynamic graph
+  - Pruning: [Tutorial](dygraph_docs/), [Demo](demo/dygraph/pruning)
+  - Quantization: [Demo](demo/dygraph/quant)
+
+
 - [Advanced Tutorials](https://paddlepaddle.github.io/PaddleSlim/tutorials/index_en.html)：Tutorials about advanced usage of PaddleSlim.
+
 - [Model Zoo](https://paddlepaddle.github.io/PaddleSlim/model_zoo_en.html)：Benchmark and pretrained models.
+
 - [API Documents](https://paddlepaddle.github.io/PaddleSlim/api_en/index_en.html)
+
 - [Algorithm Background](https://paddlepaddle.github.io/PaddleSlim/algo/algo.html): Introduce the background of quantization, pruning, distillation, NAS.
+
 - [PaddleDetection](https://github.com/PaddlePaddle/PaddleDetection/tree/master/slim): Introduce how to use PaddleSlim in PaddleDetection library.
+
 - [PaddleSeg](https://github.com/PaddlePaddle/PaddleSeg/tree/develop/slim): Introduce how to use PaddleSlim in PaddleSeg library.
+
 - [PaddleLite](https://paddlepaddle.github.io/Paddle-Lite/): How to use PaddleLite to deploy models generated by PaddleSlim.
+
 - [TensorRT Deploy](demo/quant/deploy/TensorRT): How to use TensorRT to deploy models generated by PaddleSlim.
 
 ## Performance