Link to the Wikipedia article for two-factor authentication in the README

Author: mattrubin

README.md

@@ -5,7 +5,7 @@
 [![Build Status](https://travis-ci.org/mattrubin/authenticator.svg?branch=master)](https://travis-ci.org/mattrubin/authenticator)
 
 
-Authenticator is a simple, free, and open source two-factor authentication app. It helps keep your online accounts secure by generating unique one-time passwords, which you use in combination with your other passwords to log into supporting websites. The simple combination of the password in your head and the rotating passwords generated by the app make it much harder for anyone but you to access your accounts.
+Authenticator is a simple, free, and open source [two-factor authentication](https://en.wikipedia.org/wiki/Two-factor_authentication) app. It helps keep your online accounts secure by generating unique one-time passwords, which you use in combination with your other passwords to log into supporting websites. The simple combination of the password in your head and the rotating passwords generated by the app make it much harder for anyone but you to access your accounts.
 
 - Easy: Simple setup via QR code, ["otpauth://" URL](https://code.google.com/p/google-authenticator/wiki/KeyUriFormat), or manual entry
 - Secure: All data is stored in encrypted form on the iOS keychain