Create game_demo.md

Author: shaoxiongduan

docs/game_demo.md

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+# LittleRookChess
+![image](https://user-images.githubusercontent.com/46639847/219938353-2eaa71d0-da5c-48c8-a9fe-db2489fa1074.png)
+
+https://github.com/olikraus/u8g2/blob/master/sys/arduino/u8g2_page_buffer/LittleRookChess/LittleRookChess.ino
+# Spacetrash
+![image](https://user-images.githubusercontent.com/46639847/219938377-4b7b2d2a-34c5-4b80-8309-64dda9d56ff3.png)
+
+https://github.com/olikraus/u8g2/blob/master/sys/arduino/u8g2_page_buffer/SpaceTrash/SpaceTrash.ino
+# Snake
+![image](https://user-images.githubusercontent.com/46639847/219938397-9109618b-9a15-4677-80f2-4d8203b3e311.png)
+
+https://github.com/norbertg1/Snake-game
+# Tetris
+![image](https://user-images.githubusercontent.com/46639847/219938416-7db0a753-4cb1-4768-a68c-06e84444e2fa.png)
+
+https://github.com/Zimoslaw/TetriZimoslaw
+