[Idea] warn if the AppImage does not contain update information

The runtime should warn when executing an AppImage on the command line if the AppImage does not contain update information.

With articles like this,

> AppImage lacks a robust automatic update mechanism. Users have to manually download new AppImage binary and replace existing one to install updates. AppImage app maintainers sometimes include their own update mechanism that periodically checks updates availability on their servers or requires user intervention. Recently, AppImage developers provided a tool to update existing binaries by providing delta updates. However, it still requires downloading the update tool and manually using it with an existing AppImage binary. There is no hands-free update mechanism available for AppImage yet

we should imho proactively consider AppImages that lack update information "bad" and print warnings when one tries to execute them. Hopefully this will lead to more AppImages being created with update information.