Installation instruction (Ubuntu & other Debian-based distros):
Install the package:
sudo dpkg -i hid_xiaomi-dkms_1.0_amd64.deb
Insert the kernel module
sudo modprobe hid_xiaomi
Side buttons on your mouse should start to work immediately. But you will need to do modprobe hid_xiaomi after each reboot.
To automatically insert the module while booting add hid_xiaomi line to your /etc/modules file.