Through your distro, hopefully.
Sigil
does not directly support linux, but it does provide build instructions and everything *should* work.
In fact, linux is a bit of a sore spot for the maintainer, who has had numerous issues with specific distros e.g. The Usual Suspects: Debian, Fedora/RedHat.
Although... linux distros often stink about providing timely updates. Some, e.g. Gentoo, Arch Linux, are rolling-release and do.
As stated above, you can find unofficial debian-based packages hosted here as well -- those are usually up to date,