Minor readme update

Author: rtheunissen

README.md

@@ -4,7 +4,7 @@
 [![Scrutinizer Code Quality](https://img.shields.io/scrutinizer/g/php-ds/polyfill.svg)](https://scrutinizer-ci.com/g/php-ds/polyfill/?branch=master)
 [![Packagist](https://img.shields.io/packagist/v/php-ds/php-ds.svg)](https://packagist.org/packages/php-ds/php-ds)
 
-This is a compatibility polyfill for the *ds* extension. You should include this package as a dependency of your project
+This is a compatibility polyfill for the [extension](https://github.com/php-ds/extension). You should include this package as a dependency of your project
 to ensure that your codebase would still be functional in an environment where the extension is not installed. The polyfill will not be loaded if the extension is installed and enabled.
 
 ## Install
@@ -13,7 +13,7 @@ to ensure that your codebase would still be functional in an environment where t
 composer require php-ds/php-ds
 ```
 
-You can also just specify `"php-ds/php-ds": "^1.0"` in your `composer.json` file.
+You can also *require* that the extension be installed using `ext-ds`. 
 
 ## Test