ACPI: add documentation for deprecated /proc/acpi/battery in ACPI_PROCFS

Add documentation in Kconfig help about the move of /proc/acpi/battery
to /sys/class/power_supply when selecting ACPI_PROCFS.  This will impact
a lot of users and should be documented.
Signed-off-by: Jerome Pinot <ngc891@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/acpi/Kconfig

@@ -60,6 +60,7 @@ config ACPI_PROCFS
 	  /proc/acpi/info (/sys/modules/acpi/parameters/acpica_version)
 	  /proc/acpi/dsdt (/sys/firmware/acpi/tables/DSDT)
 	  /proc/acpi/fadt (/sys/firmware/acpi/tables/FACP)
+	  /proc/acpi/battery (/sys/class/power_supply)
 	  /proc/acpi/debug_layer (/sys/module/acpi/parameters/debug_layer)
 	  /proc/acpi/debug_level (/sys/module/acpi/parameters/debug_level)