update demo readme (open-mmlab#499)

demo/README.md

@@ -1,12 +1,35 @@
 # Demo
 
-This page provides tutorials about running demos.
+This page provides tutorials about running demos. Please click the caption for more information.
 
-<!-- TOC -->
+<br>
 
-- [2D human pose demo](2d_human_pose_demo.md)
-- [2D human whole-body pose demo](2d_wholebody_pose_demo.md)
-- [2D hand demo](2d_hand_demo.md)
-- [2D pose tracking demo](2d_pose_tracking_demo.md)
+<div align="center">
+    <img src="demo_coco.gif" width="600px" alt><br>
 
-<!-- TOC -->
+[2D human pose demo](2d_human_pose_demo.md)
+</div>
+
+<br>
+
+<div align="center">
+<img src="https://user-images.githubusercontent.com/9464825/95552839-00a61080-0a40-11eb-818c-b8dad7307217.gif" width="600px" alt><br>
+
+[2D human whole-body pose demo](2d_wholebody_pose_demo.md)
+</div>
+
+<br>
+
+<div align="center">
+    <img src="https://user-images.githubusercontent.com/11788150/109098558-8c54db00-775c-11eb-8966-85df96b23dc5.gif" width="600px" alt><br>
+
+[2D hand pose demo](2d_hand_demo.md)
+</div>
+
+<br>
+
+<div align="center">
+    <img src="https://user-images.githubusercontent.com/11788150/109099201-a93dde00-775d-11eb-9624-f9676fc0e478.gif" width="600px" alt><br>
+
+[2D pose tracking demo](2d_pose_tracking_demo.md)
+</div>