Update README.md

Author: voku

README.md

@@ -7,6 +7,7 @@ This is a experiment! Lets check and fix the php documentation automatically.
 ```bash
 git clone https://github.com/php/doc-en.git
 git clone https://github.com/php/php-src.git // optional: by default we use the PhpStorm Stubs
+git clone https://github.com/phpstan/phpstan-src.git // optional: only needed if you will check stubs from phpstan
 git clone https://github.com/voku/php-doc-fixer.git
 cd php-doc-fixer/
 composer update --prefer-dist