AppImage release

[JaxxArmstrong]

Thank you for a great application. May I recommend you package it in a AppImage format so it's easy for any Linux user to use it, please.

AppImages are very easy to create and can be set up to be automatically packaged on new releases, if choose to do so.

[Hasshu]

See also #14.

[arunsivaramanneo]

duplicate of #14