[feat] Better error message when using the updater on Linux

[corentinguilloteau]

Describe the problem

When trying to use the updater on Linux, I encountered the error Unsupported operating system or platform. The problem was that I ran my application after installing it with the .deb package and not directly from the AppImage.

I spent some time figuring out where the problem was from because this error message is the same as the error message used if target_arch or target_os is unsupported.

Describe the solution you'd like

I think using a different error message for those two cases would be really helpful.

Also, it could be profitable to add a note in the documentation to inform developers that a user on Linux need to run the AppImage if he wants to use the updater.

Alternatives considered

No response

Additional context

No response

[JonasKruckenberg]

I see this as a documentation issue, not something addressable through code, but yes you are correct we should be more forthcoming about which packaging formats support updating and which do not.

[corentinguilloteau]

Wouldn't it also be possible to add a new Error here and use it here instead of the Error::UnsupportedPlatform ?

[FabianLars]

Ideally the app wouldn't even include the updater code for non appimage bundles, but that would mean that we'd have to build the binary twice :((