Add random_compat (#796)

README.md

 * [PHP IDS](https://github.com/PHPIDS/PHPIDS) - A structured PHP security layer.
 * [PHP SSH](https://github.com/Herzult/php-ssh) - An experimental object orientated SSH wrapper library.
 * [PHPSecLib](http://phpseclib.sourceforge.net/) - A pure PHP secure communications library.
+* [random_compat](https://github.com/paragonie/random_compat) - PHP 5.x support for `random_bytes()` and `random_int()`
 * [RandomLib](https://github.com/ircmaxell/RandomLib) - A library for generating random numbers and strings.
 * [SecurityMultiTool](https://github.com/padraic/SecurityMultiTool) - A PHP security library.
 * [SensioLabs Security Check](https://security.sensiolabs.org/) - A web tool to check your Composer dependencies for security advisories.