Linux: Embed AppImage update information

[frequency403]

Discussed in #37

^{Originally posted by shuvashish76 August 24, 2026}
Request to provide .zsync file for AppImage delta updates.
Updating will take less amount of data and time due to downloading only diff.

info:

• https://github.com/AppImageCommunity/AppImageUpdate#update-information-overview
• https://github.com/AppImage/AppImageSpec/blob/master/draft.md#update-information
• https://github.com/ivan-hc/AppImage-tips#how-to-add-delta-updates

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

Lots of projects already support updating AppImage e.g: LibreWolf, KeePassXC, Sigil etc.