Include ParserOptions#parse in TS typings

lib/index.d.ts

@@ -299,6 +299,16 @@ declare namespace $RefParser {
  * A regular expression can be used to match files by their full path. A string (or array of strings) can be used to match files by their file extension. Or a function can be used to perform more complex matching logic. See the custom parser docs for details.
  */
  canParse?: boolean | RegExp | string | string[] | ((file: FileInfo) => boolean)
+
+ /**
+ * This is where the real work of a parser happens. The `parse` method accepts the same [file info object](file-info-object.md) as the `canParse` function, but rather than returning a boolean value, the `parse` method should return a JavaScript representation of the file contents. For our CSV parser, that is a two-dimensional array of lines and values. For your parser, it might be an object, a string, a custom class, or anything else.
+ *
+ * Unlike the `canParse` function, the `parse` method can also be asynchronous. This might be important if your parser needs to retrieve data from a database or if it relies on an external HTTP service to return the parsed value. You can return your asynchronous value via a [Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) or a Node.js-style error-first callback. Here are examples of both approaches:
+ */
+ parse(
+ file: FileInfo,
+ callback?: (error: Error | null, data: string | null) => any
+ ): unknown | Promise<unknown>
  }
 
  /**