Added FreeOTP as a replacement for Google Authenticator

Since Google's Authenticator app is no longer being updated under a free license, I thought it might be more fitting to advocate the use of FreeOTP. FreeOTP is based off of the open source Authenticator app, and is still being maintained under an Apache license by Red Hat. It's available on F-Droid on Android, as well as Google and Apple's app stores.

This link (https://build.phonegap.com/apps/135419/) doesn't link to a symbian and iOS app, but a symbian and webOS app. I've updated the file to fix that small typo.