Sometimes *.AppImage files won’t installed to the system applications so you need manually run it.
This is where AppImageLauncher comes, it help you integrate and launch your *.AppImage applications.
How to install?
sudo add-apt-repository ppa:appimagelauncher-team/stable
sudo apt-get update
Soon if you run *.AppImage file it wil ask you weather you only want to run it or want to integrate is as well. Choose integrate to install your applications to your system.