Need a better AppRun script to support --appimage-extract behavior

[qlibp]

APPDIR env variable is not provided after extracting the appimage via --appimage-extract. So, when trying to run AppRun, will get something like TERMINFO not found and tmux can not be invoked.

Just provide the env var APPDIR=DIRECTORY_OF_SQUASHFS before running the AppRun script, then all works fine, already tested on my ubuntu20.04 compute & ubuntu22.04 docker env