F-Droid third party repository

Please consider making a third party f-droid repo to make the app more accessible for f-droid users. This is something that other projects like collabora office are doing, see [link to repo](https://www.collaboraonline.com/blog/collabora-office-on-mobiles-supporting-password-protected-documents-and-available-on-f-droid/).

This is a low hanging fruit as it is not nearly as much work as modifying the source code to match the f-droid inclusion criteria as was discussed in #382. This way we would have a trusted repo providing automatic updates, rather the manual process of apk downloads from the releases.

I'm aware that this is already possible via the the Izzi f-droid repo but that repo contains a lot of other apps and that adds a lot of unnecessary cruft.

Start by reviewing issue #382 and the linked Collabora Office example to understand the proposed third-party F-Droid repository approach. Done means providing a trusted repository for this app with automatic updates instead of requiring users to download APKs manually.

Written by the indexing model from the issue text.