Add list of utilities

Author: wooorm

readme.md

@@ -2,7 +2,7 @@
 
 **M**ark**d**own **A**bstract **S**yntax **T**ree.
 
-***
+* * *
 
 **MDAST** discloses markdown as an abstract syntax tree.  _Abstract_
 means not all information is stored in this tree and an exact replica
@@ -867,6 +867,29 @@ Yields:
 }
 ```
 
+## List of Utilities
+
+<!--lint disable list-item-spacing-->
+
+*   [`wooorm/mdast-comment-marker`](https://github.com/wooorm/mdast-comment-marker)
+    — Parse a comment marker;
+*   [`wooorm/mdast-util-definitions`](https://github.com/wooorm/mdast-util-definitions)
+    — Find definition nodes;
+*   [`wooorm/mdast-util-heading-range`](https://github.com/wooorm/mdast-util-heading-range)
+    — Markdown heading as ranges;
+*   [`wooorm/mdast-util-heading-style`](https://github.com/wooorm/mdast-util-heading-style)
+    — Get the style of a heading node;
+*   [`anandthakker/mdast-util-inject`](https://github.com/anandthakker/mdast-util-inject)
+    — Inject a tree into another at a given heading;
+*   [`wooorm/mdast-util-to-string`](https://github.com/wooorm/mdast-util-to-string)
+    — Get the plain text content of a node;
+*   [`eush77/mdast-normalize-headings`](https://github.com/eush77/mdast-normalize-headings)
+    — Ensure at most one top-level heading is in the document;
+*   [`eush77/mdast-squeeze-paragraphs`](https://github.com/eush77/mdast-squeeze-paragraphs)
+    — Remove empty paragraphs;
+*   [`wooorm/mdast-zone`](https://github.com/wooorm/mdast-zone)
+    — HTML comments as ranges or markers.
+
 ## Related
 
 *   [remark][]