Hi. Current sd card image doesn't support raspberry pi 3. You have to install supla software manually. Please type few commands at console:
cd
git clone
https://github.com/SUPLA/raspberry
rm raspberry/ext01/boot/config.txt
sudo cp -r raspberry/ext01/* /
sudo update-rc.d supla-dev defaults
sudo nano /boot/location.txt
sudo /etc/init.d/supla-dev start
SUPLA.... Nareszcie w domu.