devicetree: hwmon: Add bindings documentation for HIH6130

Add bindings documentation for HIH6130 driver.
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/hwmon/hih6130.txt

+Honeywell Humidicon HIH-6130 humidity/temperature sensor
+--------------------------------------------------------
+
+Requires node properties:
+- compatible : "honeywell,hi6130"
+- reg : the I2C address of the device. This is 0x27.
+
+Example:
+	hih6130@27 {
+		compatible = "honeywell,hih6130";
+		reg = <0x27>;
+	};