Add example images

[gwaybio]

@jenna-tomkinson - when you get a chance, can you add example images to this repository of the following categories:

1. Vignetting examples
2. Left to right imbalance
3. Top to bottom imbalance
4. Good examples

The file structure could be:

• ic_test
• example_images
  • vignetting
  • left_to_right_imbalance
  • top_to_bottom_imbalance
  • uniform

Maybe 2-4 examples per category? Any other categories?