Fix thermometer guide headers

app/src/main/res/raw/calibrating_thermometer.md

@@ -1,17 +1,17 @@
 You can update the thermometer calibration from the thermometer settings (Trail Sense Settings > Sensors > Thermometer).
 
-# Source
+## Source
 
 On most phones, you should use this historic temperature source as it will be more accurate.
 
 - **Historic** temperature is estimated from 30 years of historical data. It's usually accurate, but not during extreme weather. You can calibrate it if it's wrong for your location.
 - **Sensor** temperature is read from the phone's built-in thermometer. It's often inaccurate because it's affected by the phone's CPU and battery. You can calibrate it to improve its accuracy. If you power off your phone for a while, you will get a more accurate reading from the sensor.
 
-## Updating recorded temperatures
+### Updating recorded temperatures
 
 If you change the temperature source to "Historic", you can choose to update all previously recorded temperatures. This will replace the old temperatures with the estimated temperature from the historic data. This is useful if you previously recorded temperatures with the sensor and then switched to historic temperatures.
 
-# Calibrating
+## Calibrating
 
 1. Reset the thermometer calibration in Trail Sense.
 2. Put your phone in a cold place for 10 minutes.