Update README.md

README.md

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-# simple-scrollspy
-Simple scrollspy without jQuery, no dependencies
+# Simple Scrollspy
+
+Simple scrollspy without jQuery, no dependencies and lightweight. Only 1.94Kb.
+
+## Install
+You can install by `npm` or download inject `simple-scrollspy.js` file into your HTML code:
+```npm
+npm install simple-scrollspy
+```
+```html
+<script src="/path/to/dist/simple-scrollspy.js"></script>
+```
+
+## Usages
+```js
+import scrollSpy from 'simple-scrollspy'
+
+scrollSpy('#menu-list', {
+    offset: 100,
+    menuActiveTarget: '.menu__item > a',
+    sectionClass: 'body section.scrollspy',
+    activeClass: 'active'
+})
+```
+Or:
+```html
+<script src="/path/to/dist/simple-scrollspy.js"></script>
+<script>
+    window.onload = function () {
+        scrollSpy('#menu-list', {
+            offset: 100,
+            menuActiveTarget: '.menu__item > a',
+            sectionClass: 'body section.scrollspy',
+            activeClass: 'active'
+        })
+    }
+</script>
+```
+
+## Arguments
+- The first argument is your menu list selector. Type of `String|HTMLElement`.
+- The second argument is optional. Type of `Object`:
+
+| Name          | Type          | Default       | Description |
+| ------------- |:-------------:|:-------------:| :-----------|
+| `offset`      | Number        | 0             | Offset number |
+| `menuActiveTarget` | String | `li > a` | Element will be added active class |
+| `sectionClass` | String | `.scrollspy` | Query selector to your sections |
+| `activeClass` | String | `active` | Active class name |