add simple usage example to window.py

old-commit-hash: c4592e8547

common/window.py

@@ -38,3 +38,13 @@ class Window():
       if event.type == pygame.MOUSEBUTTONDOWN:
         mx, my = pygame.mouse.get_pos()
         return mx, my
+
+if __name__ == "__main__":
+  import numpy as np
+  win = Window(200, 200)
+  img = np.zeros((200,200,3), np.uint8)
+  while 1:
+    print("draw")
+    img += 1
+    win.draw(img)
+