[skip ci] Add more suggested links

Author: iluuu1994

CONTRIBUTING.md

@@ -96,6 +96,8 @@ base.
 * https://www.phpinternalsbook.com/
 * https://www.npopov.com/
 * https://wiki.php.net/internals
+* https://qa.php.net/phpt_details.php
+* Implementing a Range Operator into PHP [[1]](https://phpinternals.net/articles/implementing_a_range_operator_into_php) [[2]](https://phpinternals.net/articles/a_reimplementation_of_the_range_operator)
 * https://blog.ircmaxell.com/categories/PHP/
 
 ## Writing tests