Linux: Embed AppImage update information

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](https://github.com/TheAssassin/AppImageLauncher), [AppImageUpdate](https://github.com/AppImageCommunity/AppImageUpdate), [AppManager](https://github.com/kem-a/AppManager), [AM](https://github.com/ivan-hc/AM) etc...

Lots of projects already support updating AppImage e.g: [LibreWolf](https://librewolf.dev/librewolf/bsys6/releases), [KeePassXC](https://github.com/keepassxreboot/keepassxc/releases), [Sigil](https://github.com/Sigil-Ebook/Sigil/releases) etc.

Start with the AppImage update-information overview and AppImageSpec links in the issue, then locate the project's Linux AppImage packaging or release entry point. Done means the released AppImage artifacts provide the requested .zsync update information and are recognizable by compatible update tools.

Written by the indexing model from the issue text.