Update README.md

README.md

@@ -114,6 +114,8 @@ def check_answer(
 If you'd like to use a single image model, here's a handy function to turn `image_1` and `image_2` into a single split image:
 
 ```python
+from PIL import Image
+
 def concat_images_horizontal(
         image1: Image.Image, image2: Image.Image, include_space: bool=True, space_width: int=20, fill_color: tuple=(0, 0, 0)
         )  -> Image.Image: