Add hiqdev/php-ip-tools to README

[SilverFire]

Hi, @rlanvin!

Thanks for a great library, it's well designed and nice to work with. I've inited a new library as a toolkit on top of yours for free IP blocks calculation and IP ranges parsing. It's also well covered with PHPUnit and Infection.

If you think it's possible to put a link on it in your README for those who look for a use cases inspiration – it would be nice. Otherwise – no worries, you're doing a great job!

Thank you :)