X-AppImage-Version missing in .desktop file

It was kinda brutal to close my previous issue / "comment", but ok, as you suggested I can open another one to have a longer discussion.

1. Desktop file
Minor issue, but the `.desktop` file doesn’t include the app version, for example, `X-AppImage-Version=1.9.1`. It’s not a big deal since this is a terminal app, but there are third-party solutions that rely on that information to detect the installed app version and integrate with the desktop environment. The AppImage also doesn’t include any application metadata.

2. `appimagetool` zsync support
`appimagetool` isn’t distributed with zsync support. This is also a minor issue, but I had the impression that zsync updates were a major selling point of AppImages. If the AppImage ecosystem (or appstream tooling) doesn’t support it, it sends the message that zsync is effectively not useful.