free dymanically allocated memory using free
struct pixel **read_pixel_array(FILE *image, int pixel_array_offset, int width, int height) {
    // 1.
    struct pixel **pixels = malloc(sizeof(struct pixel *) * height);

    // 2.
    for (int i=0; i < height; i++) {
        pixels[i] = malloc(sizeof(struct pixel) * width);
    }

}