docs: update

README.md

@@ -252,3 +252,7 @@ with the following keys.
 | `tec_i`        | Amperes         | TEC output current feedback derived from `i_tec`     |
 | `tec_u_meas`   | Volts           | Measurement of the voltage across the TEC            |
 | `pid_output`   | Amperes         | PID control output                                   |
+
+## PID Tuning
+
+The thermostat implements a PID control loop for each of the TEC channels, more details on setting up the PID control loop can be found [here](./documentation/PID%20tuning.md).

documentation/Hardware setup.md

@@ -0,0 +1,3 @@
+# Hardware Setup
+
+## 

documentation/PID tuning.md

@@ -1,5 +1,9 @@
 # PID Tuning
 
+## Note on hardware setup
+
+When using a TEC module with the Thermostat, the Thermostat expects the thermal load (where the thermistor is connected) to heat up when a positive current flow from the TEC + terminal, through the TEC, to the TEC - terminal, and vice versa.
+
 ## Real time plot
 
 When tuning Thermostat PID parameters, it is helpful to view the temperature, PID output and other data in the form of a real time graph.