Update README.md

Author: petrknap

README.md

@@ -3,5 +3,31 @@
 Enumerated type for PHP by [Petr Knap].
 
 
+## What is enum?
+
+### Usage of php-enum
+
+```php
+// TODO make example
+```
+
+
+## How to install
+
+Run `composer require petrknap/php-enum` or merge this JSON code with your project `composer.json` file manually and run `composer install`. Instead of `dev-master` you can use [one of released versions].
+
+```json
+{
+    "require": {
+        "petrknap/php-enum": "dev-master"
+    }
+}
+```
+
+Or manually clone this repository via `git clone https://github.com/petrknap/php-enum.git` or download [this repository as ZIP] and extract files into your project.
+
+
 
 [Petr Knap]:http://petrknap.cz/
+[one of released versions]:https://github.com/petrknap/php-enum/releases
+[this repository as ZIP]:https://github.com/petrknap/php-enum/archive/master.zip