Supporte AppImage with https://github.com/StratusFearMe21/cargo-appimage

[yjpark]

follow the readme, and run cargo appimage --features=native can build the image properly, but the CWD in a temp folder when run it, and the binary file was renamed to usr/bin/bin
Can check this case, and get the assets path from executable path

Though the bevy part also need to be changed to handle this, guess have to create a patch, or can change the executable path in image, not sure whether that's possible or not.

Need to fork cargo-appimage to change the hard-coded path, which should be relatively easy to do.