Add Tutanota to F-Droid repository

Tutanota, an end-to-end encrypted email service, has an Android client with a GPLv3 license:

https://github.com/tutao/tutanota

Information on third party licenses is available here:

https://github.com/tutao/tutanota/blob/master/third-party.txt

EDIT: I've posted this in the wrong place, and they are working on a new app anyway. "We plan to add our new app (currently in implementation) to F-Droid."