Add image downloading in case colab env

[amrzv]

Hi.
In inpaint.ipynb notebook in case running in colab image grass.png is needed. So I add a cell with downloading an image in case the notebook is running in colab:

if 'COLAB_GPU' in os.environ:
  !wget https://raw.githubusercontent.com/openai/glide-text2im/main/notebooks/grass.png

[woctezuma]

• inpaint notebook error #22