Update README

Author: scriptex

README.md

@@ -1,2 +1,46 @@
-# accordion
-Front-end Accordion widget using max-height
+# Accordion
+
+Front-end accordion widget using max-height written in vanilla ES2017
+
+## Install
+
+```
+npm i @three11/accordion
+```
+
+or
+
+```
+yarn add @three11/accordion
+```
+
+## Usage
+
+First, `import` the module:
+
+```
+import Accordion from '@three11/accordion';
+```
+
+Then initialize a new instance of the module:
+
+```
+const el = doc.querySelector('[data-accordion]');
+const accordion = new Accordion(el, settings = {});
+```
+
+## Settings
+
+The default settings are:
+
+```
+headSelector: '[data-title]',   // Selector for the head element
+bodySelector: '[data-content]', // Selector for the body element
+hiddenClass:  'is--hidden',     // Hidden class name
+activeClass:  'is--active',     // Active class name
+```
+
+## License
+
+GNU GENERAL PUBLIC LICENSE
+Version 3, 29 June 2007