Update README.md

README.md

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+[![clasp](https://img.shields.io/badge/built%20with-clasp-4285f4.svg)](https://github.com/google/clasp)
+[![JavaScript Style Guide](https://img.shields.io/badge/code_style-standard-brightgreen.svg)](https://standardjs.com)
+
 # HtmlParser
+HTML Parser for Googe Apps Script
+
+## Usage
+### Add library
+project key: `1gMNYu6-SlYdKbfFMSXZz718quQVgll-qKhNobIaJwMVYL_9EgZ9GQlmp`
+
+### Use in your script
+Example:
+
+```js
+var html = UrlFetchApp.fetch('http://en.wikipedia.org/wiki/Document_Object_Model').getContentText()
+var doc = XmlService.parse(html)
+var rootElement = doc.getRootElement()
+
+var parser = HtmlParser.of(rootElement)
+var element = parser.getElementById('firstHeading')
+```
+
+## API
+API is inspired by [Document](https://developer.mozilla.org/en-US/docs/Web/API/Document).
+
+### getElementById(id)
+```js
+var element = parser.getElementById('firstHeading')
+```
+
+### getElementsByClassName(className)
+```js
+var elements = parser.getElementsByClassName('firstHeading')
+```
+
+### getElementsByTagName(tagName)
+```js
+var elements = parser.getElementsByTagName('h1')
+```
+
+## Reference
+* [Parsing HTML - Google Apps Script Examples](https://sites.google.com/site/scriptsexamples/learn-by-example/parsing-html)