The best method depends on a couple things: What kind of temperature sensor, and what you want to do with the data. If it’s an analog sensor, you might want to use pin PA5 as an input (pin 35 of the IC), which is not otherwise used.
As far as the software goes, it again depends what you’re trying to do. One easy way would be to put the display routine in place of one of the features that you’re not using, like the 5 letter words, for example.
