Impute TIFF xres/yres from withMetadata({density})

lib/output.js

@@ -637,6 +637,8 @@ function trySetAnimationOptions (source, target) {
 /**
  * Use these TIFF options for output image.
  *
+ * The `density` can be set in pixels/inch via {@link withMetadata} instead of providing `xres` and `yres` in pixels/mm.
+ *
  * @example
  * // Convert SVG input to LZW-compressed, 1 bit per pixel TIFF output
  * sharp('input.svg')