Auto-update (and Debian repository)

Shipping the .deb files in a Debian repository would allow auto-updating the application on all Debian and Ubuntu based platforms (which together account for the vast majority of distributions used). This would make the update process easier, more convenient and possibly more secure for the users, it would also integrate in GUI update managers and it would make updating through the CLI possible without running scripts which would benefit only more advanced users anyway.

AppImage files are also able to auto-update so that should be implemented.

I don't know how the auto-update mechanism could be implemented with the zip file, but there are software that are installed by extracting a zipped folder and update themselves automatically (e.g. the Tor Browser), so it should be possible to do it.

As for Android, the app is distributed through the [IzzyonDroid](https://apt.izzysoft.de/fdroid/index/apk/net.activitywatch.android) repo, but it seems to be outdated. It should be either updated on IzzyonDroid or distributed on the main F-Droid repository (running a custom F-Droid repo is also a possibility, but having the app on a more popular repo would give it more visibility). It would also be nice to offer the users who don't have Google software on their devices a way to get the app without resorting to the PlayStore (the apk file should also be included under Assets in the Releases page.

Without automatic updates people will forget to update the application, this could result in a buggy experience for the user and in useless bugreports.