* Add a Dockerfile to this repo for self-contained easy releases.
Run it from an x86_64 Linux host and it will produce 64-bit and
32-bit Linux (rpm, deb, AppImage, tar.gz) and Windows releases.
* The `make appimage` command is more self-sufficient: it will
download the appimagetool-x86_64.AppImage program for your $ARCH
for an easy no-dependencies run after you have run `make dist`
