A PT100 is a commonly used RTD. Compared to how Thermistor class works - it handles NTC's PT100 is PTC so the change in resistance with temperature is “other way around”. PT100 also have very different curve than NTCs handled by Thermistor class.
PTC means positive temperature coefficient so electrical resistance increases with raising temperature. They cannot be used as-is, you must use an amplifier circuit so they become usable by SmoothieBoard.
Currently Smoothie only supports E3D's PT100 amplifier board. Other PT100 amplifiers may be supported later (i.e. MAX31865 via SPI).
If you do not have AVCC/AGND pins, you can use 3.3V and GND. However this may introduce noise in the ADC system and may affect all temperature readings from analog sources (i.e. thermistors and PT100).
DO NOT power from 5v or you will kill the port.
You wire a PT100 almost the same way you would a thermistor, but you need to specify Smoothie it is a PT100 and where you connected the amplifier signal output:
temperature_control.hotend.enable true temperature_control.hotend.sensor pt100_e3d temperature_control.hotend.e3d_amplifier_pin 1.30 # must be a free ADC pin, not a temperature input