update doc

Author: yifanfeng97

README.md

@@ -90,9 +90,11 @@ If you find any bugs, please report it to us in [GitHub Issues](https://github.c
 
 You can draw the graph, hypergraph, directed graph, and bipartite graph with DHG's visualization tool. More details see the [Tutorial](https://deephypergraph.readthedocs.io/en/latest/tutorial/vis_structure.html)
 
-<center>
+<!-- <center>
 <img src="docs/source/_static/img/vis_graph.png" width="300"><img src="docs/source/_static/img/vis_hypergraph.png" width="300">
-</center>
+</center> -->
+
+![graph visualization](docs/source/_static/img/vis_graph.png)![hypergraph visualization](docs/source/_static/img/vis_hypergraph.png)
 
 ```python
 import matplotlib.pyplot as plt