Improve F-Droid listing

[mueller-ma]

I've seen this app on F-Droid, but it lacks screenshots, changelog and a translatable description there. It's pretty easy for you to add these information. Please have a look at this example or at the F-Droid docs or fastlane docs.
After you have commited these files to your repo and tagged a new version, you need to remove the Description and Summary from the metadata file in the F-Droid Data repo.

[hrj]

@Bubu Do you want to take a crack at this? I suppose you will have to make the change in your repo, but if you want it to be merged in here as well, please send in a PR.

[Bubu]

Most of this work should be done upstream first I think and then slightly adapted to fit this fork. Upstrema issue: element-hq#2298