build an appimage

[Reimar Bauer]

By https://appimage.org/ we can build a linux app which runs everywhere without the need to add it to one of the several linux distributions.

AppImage provides a way for upstream developers to provide “native” binaries for Linux users just the same way they could do for other operating systems.

https://docs.appimage.org/introduction/index.html

example for a conda-forge application by https://github.com/FreeCAD/FreeCAD_Conda/blob/master/utils/appimage/freecad_app_image.sh