docs: hwmon: Add documentaion for acbel-fsg032 PSU

Add documentation changes for acbel-fsg032 psu

Signed-off-by: Lakshmi Yadlapati <lakshmiy@us.ibm.com>
Link: https://lore.kernel.org/r/20230413132627.3444119-5-lakshmiy@us.ibm.com
[groeck: Fixed alphabetic order in index.rst]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>