update readme

Author: yifanfeng97

README.md

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 ![license](https://img.shields.io/hexpm/l/plug)
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-**[Website](https://deephypergraph.com/)** | **[Documentation]()** | **[Tutorials]()** | **[Official Examples]()**
+**[Website](https://deephypergraph.com/)** | **[Documentation](https://deephypergraph.readthedocs.io/en/latest/)** | **[Tutorials]()** | **[Official Examples]()**
 
 
 **DHG** *(DeepHypergraph)* is a deep learning library built upon [PyTorch](https://pytorch.org) for learning with both Graph Neural Networks and Hypergraph Neural Networks. It is a general framework that supports both low-order and high-order message passing like **from vertex to vertex**, **from vertex in one domain to vertex in another domain**, **from vertex to hyperedge**, **from hyperedge to vertex**, **from vertex set to vertex set**.