hwmon: (w83773g) Add documentation

Add documentation for the w83773g driver.
Signed-off-by: Lei YU <mine260309@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/w83773g

+Kernel driver w83773g
+====================
+
+Supported chips:
+  * Nuvoton W83773G
+    Prefix: 'w83773g'
+    Addresses scanned: I2C 0x4c and 0x4d
+    Datasheet: https://www.nuvoton.com/resource-files/W83773G_SG_DatasheetV1_2.pdf
+
+Authors:
+	Lei YU <mine260309@gmail.com>
+
+Description
+-----------
+
+This driver implements support for Nuvoton W83773G temperature sensor
+chip. This chip implements one local and two remote sensors.
+The chip also features offsets for the two remote sensors which get added to
+the input readings. The chip does all the scaling by itself and the driver
+therefore reports true temperatures that don't need any user-space adjustments.
+Temperature is measured in degrees Celsius.
+The chip is wired over I2C/SMBus and specified over a temperature
+range of -40 to +125 degrees Celsius (for local sensor) and -40 to +127
+degrees Celsius (for remote sensors).
+Resolution for both the local and remote channels is 0.125 degree C.
+
+The chip supports only temperature measurement. The driver exports
+the temperature values via the following sysfs files:
+
+temp[1-3]_input
+temp[2-3]_fault
+temp[2-3]_offset
+update_interval