hwmon: (sch5627) Document behaviour of limit registers

The values of the limit registers affect the fan speed in a
particular way. Document this behaviour so that future users
can exploit it if required.

Signed-off-by: Armin Wolf <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>

Documentation/hwmon/sch5627.rst

···
 through an embedded microcontroller. An application note describing the
 protocol for communicating with the microcontroller is available upon
 request. Please mail me if you want a copy.
+
+
+Controlling fan speed
+---------------------
+
+The SCH5627 allows for partially controlling the fan speed. If a temperature
+channel excedes tempX_max, all fans are forced to maximum speed. The same is not
+true for tempX_crit, presumably some other measures to cool down the system are
+take in this case.
+In which way the value of fanX_min affects the fan speed is currently unknown.