doc: add missing options.info for ZstdOptions

Source code of `class Zstd` calls ctor of parent `ZlibBase` via
`super()`

By inspecting `opts` in `ZlibBase` ctor, we can see `opts?.info` is
further used to determine the return shapes of `*Sync()` methods in
children class. This information will need to be revealed in nodejs doc.

This PR is separated from the one for `BrotliOptions`, since these two
changes potentially need to be backported to different minimum versions.

PR-URL: #58360
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: hkleungai

doc/api/zlib.md

@@ -1069,6 +1069,7 @@ Each Zstd-based class takes an `options` object. All options are optional.
 * `params` {Object} Key-value object containing indexed [Zstd parameters][].
 * `maxOutputLength` {integer} Limits output size when using
   [convenience methods][]. **Default:** [`buffer.kMaxLength`][]
+* `info` {boolean} If `true`, returns an object with `buffer` and `engine`. **Default:** `false`
 
 For example: