Fix docs' misinformation about Google Authenticator not supporting sync between devices

[Toreno96]

In the README's section about the Google Authenticator, there's info that:

The main issue with this app is that it does not offer any way to backup the secrets, and synchronize them between the
devices.

This is not true anymore, as according to the app's official changelog, it is now possible to move accounts between the devices (although, I didn't check the details yet on how good it works).

We should update the README, then.