Add note to zulip app noting that this version doesn't have notifications

Thanks @Licaon_Kter - it looks like we’re chatting across multiple platforms now

I think I’m not understanding why Add minimal Fastlane by licaon-kter · Pull Request #1632 · zulip/zulip-flutter · GitHub is blocking here?

As I just suggested here, would it make sense (/would it be possible) to add something into the F-Droid build process so that it only shows on the F-Droid version?