Edit soruce.list:
nano /etc/apt/sources.list
append line to source.list
deb http://apt.tvheadend.org/unstable/ jessie main
Save and exit
Run update
apt-get update
apt-get install tvheadend -y
(your will be prompted for admin username and password
Installation done.
On a browser - go to
http://<pi-ip>:9981
login with admin and password used at install
Follow instructions