hwmon: (coretemp) Add comments describing the handling of HT CPUs

The coretemp driver provides a single set of device attributes for each
physical core of a HT CPU to avoid duplicate sensors.  This
functionality was introduced with commit d883b9f0 ("hwmon:
(coretemp) Skip duplicate CPU entries").

Commit e40cc4bd

 ("x86/hwmon: register alternate sibling upon CPU
removal") extends this functionality to register the HT sibling of a CPU
which is taken offline, to ensure that sensor attributes are provided if
at least one HT sibling of a core is online.

Add comments into the code describing the functionality in some more
detail.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>