function srcset(image, sizes = []) {
  return sizes.map(size => `${src(image, size)} ${size}w`).join(', ');
}
Generates the srcset attribute value for an image with different sizes.
@param {string} image - The original image URL.
@param {number[]} sizes - The array of sizes for the image.
@returns {string} - The srcset attribute value.