Add improved docs

lib/index.js

@@ -48,12 +48,12 @@
  *   Do not use an extra space when closing self-closing elements: `<img/>`
  *   instead of `<img />`.
  * @property {number | null | undefined} [printWidth=Infinity]
- *   Specify the line length that the printer will wrap on.
- *   This is not a hard maximum width: things will be printed longer and
- *   shorter.
+ *   Try and wrap syntax at this width.
  *
- *   Note: this option is only used for JSX tags currently, and might be moved
- *   to `mdast-util-to-markdown` in the future.
+ *   When set to a finite number (say, `80`), the formatter will print
+ *   attributes on separate lines when a tag doesn’t fit on one line.
+ *   The normal behavior is to print attributes with spaces between them
+ *   instead of line endings.
  */
 
 import {ccount} from 'ccount'
@@ -473,6 +473,10 @@ export function mdxJsxFromMarkdown() {
 /**
  * Create an extension for `mdast-util-to-markdown` to enable MDX JSX.
  *
+ * This extension configures `mdast-util-to-markdown` with
+ * `options.fences: true` and `options.resourceLink: true` too, do not
+ * overwrite them!
+ *
  * @param {ToMarkdownOptions | null | undefined} [options]
  *   Configuration.
  * @returns {ToMarkdownExtension}