Docs: add example of how to get the right-side-up width/height (lovel…

…l#3127)

See lovell#3124

lib/input.js

@@ -299,8 +299,8 @@ function _isStreamInput () {
  *
  * - `format`: Name of decoder used to decompress image data e.g. `jpeg`, `png`, `webp`, `gif`, `svg`
  * - `size`: Total size of image in bytes, for Stream and Buffer input only
- * - `width`: Number of pixels wide (EXIF orientation is not taken into consideration)
- * - `height`: Number of pixels high (EXIF orientation is not taken into consideration)
+ * - `width`: Number of pixels wide (EXIF orientation is not taken into consideration, see example below)
+ * - `height`: Number of pixels high (EXIF orientation is not taken into consideration, see example below)
  * - `space`: Name of colour space interpretation e.g. `srgb`, `rgb`, `cmyk`, `lab`, `b-w` [...](https://libvips.github.io/libvips/API/current/VipsImage.html#VipsInterpretation)
  * - `channels`: Number of bands e.g. `3` for sRGB, `4` for CMYK
  * - `depth`: Name of pixel depth format e.g. `uchar`, `char`, `ushort`, `float` [...](https://libvips.github.io/libvips/API/current/VipsImage.html#VipsBandFormat)
@@ -343,6 +343,17 @@ function _isStreamInput () {
  *     // data contains a WebP image half the width and height of the original JPEG
  *   });
  *
+ * @example
+ * // Based on EXIF rotation metadata, get the right-side-up width and height:
+ *
+ * const size = getNormalSize(await sharp(input).metadata());
+ *
+ * function getNormalSize({ width, height, orientation }) {
+ *   return orientation || 0 >= 5
+ *     ? { width: height, height: width }
+ *     : { width, height };
+ * }
+ *
  * @param {Function} [callback] - called with the arguments `(err, metadata)`
  * @returns {Promise<Object>|Sharp}
  */