Add changelog on F-Droid

[scollovati]

Describe the solution you'd like
It may be useful to create the changelog in the proper format so that it is parsed by F-Droid website and app.

Additional context
Currently no changelog appears: https://f-droid.org/it/packages/com.standardnotes/

ProtonVPN for example has it: https://f-droid.org/it/packages/ch.protonvpn.android/