Add F-Droid download badge to website

[rugk]

Is your feature request related to a problem? Please describe.
I visited https://timecop.app/de/ and thought your Android app is only available for Google Play.
Browsing this repository I noticed it is available on F-Droid, too.

Describe the solution you'd like
It would be great to have a download button or at least a link on your download page at

Herr you can get a download badge: https://fdroid.gitlab.io/artwork/badge/get-it-on.png

Describe alternatives you've considered
A link?

Additional context