That code is card config, so you add a card, switch to YAML, and then add the code.
Yes, in the meantime, I discovered more detailed instructions at How-To Geek, but the YAML listed there gave errors - I think that some indentations are incorrect. However, the YAML listed at github works just fine …
Now that I have it all working, I just have to interpret the results and improve my HA rating … 