write README

Author: mehm8128

README.md

@@ -1,7 +1,41 @@
 # rehype-toc
 
+[![CI on main](https://github.com/mehm8128/rehype-toc/actions/workflows/main.yml/badge.svg)](https://github.com/mehm8128/rehype-toc/actions/workflows/main.yml)
+[![NPM Version](https://img.shields.io/npm/v/@mehm8128/rehype-toc)](https://www.npmjs.com/package/@mehm8128/rehype-toc)
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
+
 rehype plugin to generate a table of contents from headings in your markdown.
 
 You can create the table of contents such below.
 
 ![A table of contents whose each items are anchor link.](assets/toc.png)
+
+## Installation
+
+```bash
+pnpm install @mehm8128/rehype-toc
+```
+
+## Usage
+
+### astro.config.mjs
+
+```ts
+import { rehypeCollapsableToc } from "@mehm8128/rehype-toc";
+
+export default defineConfig({
+  markdown: {
+    rehypePlugins: [rehypeCollapsableToc],
+  },
+});
+```
+
+### rehype
+
+```ts
+import { rehype } from "rehype"
+import { rehypeCollapsableToc } from "@mehm8128/rehype-toc";
+
+const input = "<h2 id="heading-id"><a href="#heading-id">Heading</a></h2>";
+const { value } = await rehype().use(rehypeCollapsableToc).process(input);
+```