hwmon: Document the new fan1_target interface file

Signed-off-by: Jean Delvare <khali@linux-fr.org>
diff --git a/Documentation/hwmon/sysfs-interface b/Documentation/hwmon/sysfs-interface
index d73d2e8..a9a18ad 100644
--- a/Documentation/hwmon/sysfs-interface
+++ b/Documentation/hwmon/sysfs-interface
@@ -152,6 +152,13 @@
 		Note that this is actually an internal clock divisor, which
 		affects the measurable speed range, not the read value.
 
+fan[1-*]_target
+		Desired fan speed
+		Unit: revolution/min (RPM)
+		RW
+		Only makes sense if the chip supports closed-loop fan speed
+		control based on the measured fan speed.
+
 Also see the Alarms section for status flags associated with fans.