[v2.0] Update README example args

[LevGun]

It seems that the middle parameter was removed from this function:

# Compress the image
compressed_img_data = compress_image(img, "rgb", 15000)  # Compress to 15000 bytes in RGB format

It has become:

# Compress the image
compressed_img_data = compress_image(img, 15000)  # Compress to 15000 bytes in RGB format