Add Halite to security list

Provides industry standard encryption using modern cryptography standards.

README.md

 * [Zed](https://www.owasp.org/index.php/OWASP_Zed_Attack_Proxy_Project) - An integrated penetration testing tool for web applications.
 * [VAddy](http://vaddy.net) - A continuous security testing platform for web applications.
 * [Optimus](https://github.com/jenssegers/optimus) - Id obfuscation based on Knuth's multiplicative hashing method.
+* [Halite](https://paragonie.com/project/halite) - A simple library for encryption using [libsodium](https://github.com/jedisct1/libsodium).
 
 ## Passwords
 *Libraries and tools for working with and storing passwords.*