improve readme

Author: Daniel Gomes

README.md

@@ -1,8 +1,18 @@
 # Minimalist and Typed Immutable Collections for PHP
-[![Build Status](https://travis-ci.org/dcsg/php-immutable-collections.svg?branch=master)](https://travis-ci.org/dcsg/php-immutable-collections) [![SymfonyInsight](https://insight.symfony.com/projects/159123de-9d05-4af3-a650-6e8ea7aadaea/mini.svg)](https://insight.symfony.com/projects/159123de-9d05-4af3-a650-6e8ea7aadaea)
+[![Build Status](https://travis-ci.org/dcsg/php-immutable-collections.svg?branch=master)](https://travis-ci.org/dcsg/php-immutable-collections) [![SymfonyInsight](https://insight.symfony.com/projects/8cc27627-24e7-407c-9839-766c9946eb2c/mini.svg)](https://insight.symfony.com/projects/8cc27627-24e7-407c-9839-766c9946eb2c)
 
 A library that provides a set of minimalist, typed and piped Immutable Collections for PHP.
 
+###### Requirements
+
+PHP > 7.1
+
+###### Installation
+
+```bash
+composer require dcsg/php-immutable-collections
+```
+
 #### What Problems does this solve?
 
 * Immutable List Collection
@@ -42,12 +52,6 @@ This way you have the possibility to use them and extend it's behavior tailored
 
 #### Basic usage
 
-##### Installation
-
-```bash
-composer require dcsg/php-immutable-collections
-```
-
 ###### Creating a Typed List Collection
 
 ```php