docs: flesh out README with usage, badges, and docs links

README.md

@@ -2,16 +2,120 @@
 
 > Resolves every import and produces a fully deterministic hash for any entry file.
 
+[![npm version](https://img.shields.io/npm/v/@maastrich/hashup.svg?style=flat-square)](https://www.npmjs.com/package/@maastrich/hashup)
+[![npm downloads](https://img.shields.io/npm/dm/@maastrich/hashup.svg?style=flat-square)](https://www.npmjs.com/package/@maastrich/hashup)
+[![bundle size](https://img.shields.io/bundlephobia/minzip/@maastrich/hashup?style=flat-square)](https://bundlephobia.com/package/@maastrich/hashup)
+[![install size](https://packagephobia.com/badge?p=@maastrich/hashup)](https://packagephobia.com/result?p=@maastrich/hashup)
+[![license](https://img.shields.io/npm/l/@maastrich/hashup.svg?style=flat-square)](./LICENSE)
+[![node](https://img.shields.io/node/v/@maastrich/hashup.svg?style=flat-square)](https://nodejs.org)
+[![GitHub stars](https://img.shields.io/github/stars/maastrich/hashup?style=flat-square)](https://github.com/maastrich/hashup/stargazers)
+
+`hashup` walks every `import` reachable from a given entry file — respecting
+`tsconfig` paths, package exports, and conditional imports — and produces a
+stable SHA-256 hash of the combined graph. Use it as a cache key, a build
+invalidation signal, or a content-addressed fingerprint for a module.
+
+## Features
+
+- **Fully deterministic** — same inputs always produce the same SHA-256 hash.
+- **Transitive resolution** — walks the full import graph via `enhanced-resolve`.
+- **Multi-format** — `.ts`, `.tsx`, `.js`, `.jsx`, `.mjs`, `.mts`, `.cjs`, `.json`, and more.
+- **Extras** — include arbitrary files (lockfiles, configs) in the hash.
+- **Library or CLI** — call `hashup()` from Node, or run the `hashup` binary
+  against a `hashup.json` with any number of named entries.
+
 ## Installation
 
 ```bash
 npm install @maastrich/hashup
+# or
+pnpm add @maastrich/hashup
+# or
+yarn add @maastrich/hashup
 ```
 
+Requires Node.js `>= 18`. ESM-only.
+
 ## Usage
 
-Coming soon.
+### Library
+
+```ts
+import { hashup } from "@maastrich/hashup";
+
+const { hash, files } = await hashup("./src/index.ts");
+
+console.log(hash); // "48adf62a70c2645d0fc15ee3060973245af5dc30a542372791a7e1f05eaeacf6"
+console.log(files.length); // number of resolved files
+```
+
+Include files outside the import graph (lockfiles, configs) via `extras`:
+
+```ts
+await hashup("./src/index.ts", {
+  extras: ["./package.json", "./pnpm-lock.yaml"],
+});
+```
+
+### CLI
+
+Drop a `hashup.json` at the root of your project:
+
+```json
+{
+  "$schema": "https://maastrich.github.io/hashup/schema.json",
+  "baseDir": ".",
+  "entries": {
+    "app": { "entry": "src/index.ts", "extras": ["package.json"] },
+    "worker": { "entry": "src/worker.ts" }
+  }
+}
+```
+
+Then run:
+
+```bash
+$ hashup
+app     48adf62a70c2645d0fc15ee3060973245af5dc30a542372791a7e1f05eaeacf6
+worker  0c4b8d9f…
+```
+
+Other modes:
+
+```bash
+hashup --json              # machine-readable output
+hashup --json --files      # include the resolved file list
+hashup src/index.ts        # one-off, skip the config file
+hashup -c build.hashup.json
+```
+
+Flags: `-c/--config <path>`, `-b/--base-dir <dir>`, `-e/--extra <file>`
+(single-file mode, repeatable), `--json`, `--files`, `-h/--help`.
+
+## Documentation
+
+Full docs live at **<https://maastrich.github.io/hashup>**:
+
+- [Getting started](https://maastrich.github.io/hashup/guide/getting-started)
+- [Usage patterns](https://maastrich.github.io/hashup/guide/usage)
+- [CLI & config reference](https://maastrich.github.io/hashup/guide/cli)
+- [How it works](https://maastrich.github.io/hashup/guide/how-it-works)
+- [API reference](https://maastrich.github.io/hashup/api/)
+
+## Contributing
+
+Issues and PRs welcome. The repo uses [Vite+](https://viteplus.dev) — use `vp`
+for everything:
+
+```bash
+vp install      # install dependencies
+vp check        # format + lint + type-check
+vp test         # run tests
+vp pack         # build
+```
+
+See [`AGENTS.md`](./AGENTS.md) for repo conventions.
 
 ## License
 
-MIT © [Mathis Pinsault](https://github.com/maastrich)
+[MIT](./LICENSE) © [Mathis Pinsault](https://github.com/maastrich)