apt-get install -y openvpn
cd /etc/openvpn
wget http://www.privateinternetaccess.com/openvpn/openvpn.zip
unzip openvpn.zip
cp UK\ London.ovpn pia.conf

Edit /etc/default/openvpn to include

AUTOSTART="pia"

Edit /etc/openvpn/pia.conf to include

auth-user-pass .secrets
log-append /var/log/openvpn.log

then /epc/openvpn/.secrets is chmod 600 and contains

my_username
my_password

Start manually with openvpn pia.conf to test. Start the service with service openvpn start But it should boot automatically.