feat(README): add usage

packages/xo-acl-resolver/README.md

@@ -12,7 +12,29 @@ Installation of the [npm package](https://npmjs.org/package/xo-acl-resolver):
 
 ## Usage
 
-**TODO**
+```js
+import check from 'xo-acl-resolver'
+
+// This object contains a list of permissions returned from
+// xo-server's acl.getCurrentPermissions.
+const permissions = { /* ... */ }
+
+// This function should returns synchronously an object from an id.
+const getObject = id => { /* ... */ }
+
+// For a single object:
+if (check(permissions, getObject, objectId, permission)) {
+  console.log(`${permission} set for object ${objectId}`)
+}
+
+// For multiple objects/permissions:
+if (check(permissions, getObject, [
+  [ object1Id, permission1 ],
+  [ object12d, permission2 ],
+])) {
+  console.log('all permissions checked')
+}
+```
 
 ## Development