Updated README for new pwm-gpio-fan overlay

Updated README for new pwm-gpio-fan overlay
Signed-off-by: Kai-Uwe Herbing <[email protected]>

Author: herbingk

arch/arm/boot/dts/overlays/README

@@ -4036,6 +4036,35 @@ Load:   dtoverlay=pwm-gpio,<param>=<val>
 Params: gpio                    Output pin (default 4)
 
 
+Info:   Configure a GPIO connected PWM cooling fan controlled by the software-based
+        GPIO PWM kernel module
+Load:   dtoverlay=pwm-gpio-fan,<param>=<val>
+Params: fan_gpio                BCM number of the pin driving the fan, default 18 (GPIO 18)
+        fan_temp0               CPU temperature at which fan is started with low speed
+                                in millicelsius, default 55000 (55 °C)
+        fan_temp1               CPU temperature at which fan is switched to medium speed
+                                in millicelsius, default 60000 (60 °C)
+        fan_temp2               CPU temperature at which fan is switched to high speed
+                                in millicelsius, default 67500 (67.5 °C)
+        fan_temp3               CPU temperature at which fan is switched to max speed
+                                in millicelsius, default 75000 (75 °C)
+        fan_temp0_hyst          Temperature hysteris at which fan is stopped in millicelsius,
+                                default 5000 (resulting in 50 °C)
+        fan_temp1_hyst          Temperature hysteris at which fan is switched back to low speed
+                                in millicelsius, default 5000 (resulting in 55 °C)
+        fan_temp2_hyst          Temperature hysteris at which fan is switched back to medium speed
+                                in millicelsius, default 5000 (resulting in 62.5 °C)
+        fan_temp3_hyst          Temperature hysteris at which fan is switched back to high speed
+                                in millicelsius, default 5000 (resulting in 70 °C)
+        fan_temp0_speed         Fan speed for low cooling state in range 0 to 255,
+                                default 114 (45% PWM duty cycle)
+        fan_temp1_speed         Fan speed for medium cooling state in range 0 to 255,
+                                default 152 (60% PWM duty cycle)
+        fan_temp2_speed         Fan speed for high cooling state in range 0 to 255,
+                                default 204 (80% PWM duty cycle)
+        fan_temp3_speed         Fan speed for max cooling state in range 0 to 255,
+                                default 255 (100% PWM duty cycle)
+
 Name:   pwm-ir-tx
 Info:   Use GPIO pin as pwm-assisted infrared transmitter output.
         This is an alternative to "gpio-ir-tx". pwm-ir-tx makes use