Update README.md

Author: rtheunissen

README.md

@@ -4,6 +4,10 @@
 [![Build status](https://ci.appveyor.com/api/projects/status/dbcssp6flml2gher?svg=true)](https://ci.appveyor.com/project/rtheunissen/extension)
 [![PECL](https://img.shields.io/badge/PECL-1.0.2-blue.svg)](https://pecl.php.net/package/ds)
 
+## Documentation
+
+Documentation is available on [php.net](http://docs.php.net/manual/en/book.ds.php). You can include the [polyfill](https://github.com/php-ds/polyfill) in your project for IDE integration and autocomplete support. The polyfill will not be loaded if the extension is enabled, but it's still useful to have the PHP source in your working directory.
+
 ## Installation
 
 The easiest way to install the extension is to use PECL: