update readme

Author: Zsolt Gál

README.md

@@ -1,2 +1,20 @@
 # php-cli-cross-platform-open
 Opens a file or URL in the user's preferred application in CLI (cross platform)
+
+## usage
+
+```
+<?php
+
+use Technodelight\CliOpen\OsAdaptingFactory;
+$cliOpen = OsAdaptingFactory::create();
+$cliOpen->open('https://packagist.com');
+```
+
+## requirements
+
+You need one of the following terminal applications available:
+
+- open (OS X default)
+- xdg-open (default in some linux distros)
+- opn / open-cli (https://github.com/sindresorhus/open-cli)