Add synopsis

Author: mjradwin

README.md

@@ -1,2 +1,18 @@
-# hdate-js
+# @hebcal/hdate
 converts between Hebrew and Gregorian dates
+
+[![Build Status](https://github.com/hebcal/hdate-js/actions/workflows/node.js.yml/badge.svg)](https://github.com/hebcal/hdate-js/actions/workflows/node.js.yml)
+
+# Installation
+```bash
+$ npm install @hebcal/hdate
+```
+
+## Synopsis
+```javascript
+import {greg, abs2hebrew} from '@hebcal/hdate';
+
+const date = new Date(2008, 10, 13); // 13 November 2008
+const abs = greg.greg2abs(date);
+const hdate = abs2hebrew(abs); // {yy: 5769, mm: CHESHVAN, dd: 15}
+```