Add section on related projects

Author: wooorm

readme.md

@@ -29,6 +29,7 @@ This document describes version 1.0.0 of **NLCST**.
     *   [WhiteSpace](#whitespace)
     *   [Source](#source)
     *   [TextNode](#textnode)
+*   [Related](#related)
 *   [License](#license)
 
 ## List of Utilities
@@ -152,6 +153,14 @@ interface TextNode < Text {
 }
 ```
 
+## Related
+
+*   [retext][]
+*   [unist][]
+*   [vfile][]
+*   [hast][]
+*   [mdast][]
+
 ## License
 
 MIT © Titus Wormer
@@ -171,3 +180,13 @@ MIT © Titus Wormer
 [symbol]: #symbol
 
 [changelog]: https://github.com/syntax-tree/nlcst/releases
+
+[retext]: https://github.com/wooorm/retext
+
+[vfile]: https://github.com/vfile/vfile
+
+[unist]: https://github.com/syntax-tree/unist
+
+[hast]: https://github.com/syntax-tree/hast
+
+[mdast]: https://github.com/syntax-tree/mdast