Adding phpdocumentor (#5764)

books/free-programming-books-langs.md

@@ -1605,6 +1605,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [Clean Code PHP](https://github.com/jupeter/clean-code-php)
 * [PHP 5 Power Programming](http://www.informit.com/content/images/013147149X/downloads/013147149X_book.pdf) (PDF)
 * [PHP Best Practices](https://phpbestpractices.org)
+* [PHP Documentor - Documentation](https://docs.phpdoc.org) - phpdoc.org
 * [PHP Internals Book](http://www.phpinternalsbook.com)
 * [PHP Notes for Professionals](https://goalkicker.com/PHPBook/) - Compiled from StackOverflow Documentation (PDF)
 * [PHP Pandas](http://daylerees.com/php-pandas/) - Dayle Rees