Hiri was recently made available as a snap package on Linux and that's what you should use to install Hiri if your distribution supports snaps. Otherwise, you should download and use the tarball archive.
If you run into problems please open a support ticket.
Step 1
Make sure that you have snapd installed on your system. If you're running Ubuntu 16.04 or newer, you'll have it installed by default.
If you're on Ubuntu 14.04, you'll have to install snapd (snap daemon):
sudo apt-get install snapd
If you're running a different distro, see How to install snapd on other distros.
Step 2
Install Hiri snap package:
sudo snap install hiri
Step 3
To be able to open links in emails you'll need to install snapd-xdg-open. On Ubuntu:
sudo apt-get install snapd-xdg-open
If you're not running Ubuntu, you'll have to check if this package exists on your distribution.
Step 4
Type hiri on the terminal to run the application, or use the desktop launcher to do so.
Updates
All snaps that you have installed silently update each day. So you'll always be running the latest stable version of Hiri.