docs: add usage example

README.md

@@ -1,2 +1,26 @@
-# npmrc
-.npmrc formatter
+# dotnpmrc
+> `.npmrc` formatter
+ 
+## Usage
+```ts
+import {formatNpmrc} from 'dotnpmrc'
+
+const contents = formatNpmrc({
+  format: 'npm9',
+  scopes: [{
+    name: 'example',
+    registry: 'https://npm-registry.example.com/',
+    auth: 'base64-of-username-and-password',
+    authToken: 'npmToken.bearer',
+    alwaysAuth: true,
+  }],
+  root: {
+    registry: 'https://registry.yarnpkg.com'
+  }
+})
+
+await fs.writeFile('.npmrc', contents, {encoding: 'utf8'})
+```
+
+## License
+[MIT](./LICENSE)