README: Add section on using resistive heaters

README.md

@@ -187,6 +187,12 @@ If the Thermostat is used for temperature control with the Sinara 5432 DAC "Zoti
 
 Testing heat flow direction with a low set current is recommended before installation of the TEC module.
 
+## Resistive Heater
+
+When using resistive heaters with the Thermostat, ensure that the thermal load has sufficient cooling, and connect the heater to TEC0- and TEC0+ or TEC1- and TEC1+.
+
+Then, set `max_i_neg` and `output_min` to 0 A with `pwm <ch> max_i_neg 0` and `pid <ch> output_min 0`, and make sure that `output_max` is non-negative.
+
 ### Limits
 
 Each MAX1968 TEC driver has analog/PWM inputs for setting