docs: introduction

Signed-off-by: Lexus Drumgold <unicornware@flexdevelopment.llc>

Author: unicornware

README.md

@@ -20,6 +20,7 @@ It implements the [**unist**][unist] spec.
 ## Contents
 
 - [Introduction](#introduction)
+  - [Where this specification fits](#where-this-specification-fits)
 - [Types](#types)
 - [Nodes (abstract)](#nodes-abstract)
 - [Nodes](#nodes)
@@ -30,7 +31,12 @@ It implements the [**unist**][unist] spec.
 
 ## Introduction
 
-**TODO**: introduction
+This document defines a format for representing file systems as abstract syntax trees. Development of fst started in
+January 2025. This specification is written in a [TypeScript][]-like grammar.
+
+### Where this specification fits
+
+fst extends [unist][], a format for syntax trees, to benefit from its [ecosystem of utilities](#list-of-utilities).
 
 ## Types
 
@@ -60,6 +66,11 @@ See the [unist glossary][unist-glossary] for more terms.
 
 See the [unist list of utilities][unist-utilities] for more utilities.
 
+- [`fst-util-from-fs`][fst-util-from-fs] — create trees from file systems
+- [`unist-util-builder`][unist-util-builder] — build trees
+- [`unist-util-inspect`][unist-util-inspect] — inspect trees
+- [`unist-util-visit`][unist-util-visit] — visit nodes using [preorder][] or [postorder][] traversal
+
 ## Contribute
 
 See [`CONTRIBUTING.md`](CONTRIBUTING.md).
@@ -71,7 +82,13 @@ community you agree to abide by its terms.
 
 [fst-ideas]: https://github.com/flex-development/fst/discussions/new?category=idea
 
-<!-- [fst-util-from-fs]: https://github.com/flex-development/fst-util-from-fs -->
+[fst-util-from-fs]: https://github.com/flex-development/fst-util-from-fs
+
+[postorder]: https://github.com/syntax-tree/unist#postorder
+
+[preorder]: https://github.com/syntax-tree/unist#preorder
+
+[typescript]: https://www.typescriptlang.org
 
 <!-- [unist-child]: https://github.com/syntax-tree/unist#child -->
 
@@ -91,6 +108,12 @@ community you agree to abide by its terms.
 
 <!-- [unist-tree]: https://github.com/syntax-tree/unist#tree -->
 
+[unist-util-builder]: https://github.com/flex-development/unist-util-builder
+
+[unist-util-inspect]: https://github.com/flex-development/unist-util-inspect
+
+[unist-util-visit]: https://github.com/flex-development/unist-util-visit
+
 [unist-utilities]: https://github.com/syntax-tree/unist#list-of-utilities
 
 [unist]: https://github.com/syntax-tree/unist