Linux: Embed AppImage update information

[shuvashish76]

When trying to update via AppImageUpdate

This is a common standard for updating AppImages.
AppImage having update information would also recognized by other software e.g. AppImageLauncher

info:

• https://github.com/AppImageCommunity/AppImageUpdate#update-information-overview
• https://github.com/AppImage/AppImageSpec/blob/master/draft.md#update-information

[c3er]

Thank you for reporting this issue!

I hope, that I manage to add these AppImage update information starting with the next version.

[shuvashish76]

Also do checkout this guide: https://github.com/ivan-hc/AppImage-tips

[c3er]

I'm sorry, but I'm afraid, I have to prioritize this issue down.

To try out, whether any solution works, I need to setup a proper Linux box and I currently don't have the motivation to do so (the AppImage is currently built on a WSL under Windows). Also, I introduced some regressions in version 4.0.0. And I want to finish the major restructuring one day.

I added the tag "help wanted" for the case that someone wants to contribute some solution. Also, I think this should be a "good first issue", because this shouldn't require too much knowledge about idiosyncrasies of this project.

All the release packages are built via electron-builder and there appears to exist some support for this update mechanism, see:

• Auto Update
• electron updater.Class.AppImageUpdater

If electron-builder's support turns out to be insufficient for this case, some hook is already used, that could be extended:

• build/afterPack.js: This is the place, where all files are gathered and before the actual package is being built
• build/afterAllArtifactBuild.js: Here are the packages built already