Docs: improve output format info for toBuffer

lib/output.js

@@ -82,6 +82,8 @@ function toFile (fileOut, callback) {
  * Write output to a Buffer.
  * JPEG, PNG, WebP, AVIF, TIFF, GIF and raw pixel data output are supported.
  *
+ * Use {@link toFormat} or one of the format-specific functions such as {@link jpeg}, {@link png} etc. to set the output format.
+ *
  * If no explicit format is set, the output format will match the input image, except SVG input which becomes PNG output.
  *
  * By default all metadata will be removed, which includes EXIF-based orientation.
@@ -108,6 +110,7 @@ function toFile (fileOut, callback) {
  *
  * @example
  * sharp(input)
+ *   .png()
  *   .toBuffer({ resolveWithObject: true })
  *   .then(({ data, info }) => { ... })
  *   .catch(err => { ... });