Add fastlane templates for fdroid (#772)

* Add fastlane templates for fdroid

F-Droid has a different syntax highlighting: https://f-droid.org/en/docs/Build_Metadata_Reference/#Description



I also added a sentence about the removed features.

Signed-off-by: mueller-ma <mueller-ma@users.noreply.github.com>

* Revert "Use icon from play store (#773)"

The app icon with its white background looks better than an image with
transparent background.
This reverts commit 15645762.

* Add newline in F-Droid description

Signed-off-by: mueller-ma <mueller-ma@users.noreply.github.com>

* White background in the feature graphic

Signed-off-by: mueller-ma <mueller-ma@users.noreply.github.com>

* Add badges to readme

Signed-off-by: mueller-ma <mueller-ma@users.noreply.github.com>