doc: add hyperthreading note to power library guide
doc: add hyperthreading note to power library guide

Signed-off-by: David Hunt <763be7c8e0ad91e03160e7aed76d5cd41534e2f9@intel.com>
Acked-by: Marko Kovacevic <32a723043e16bf2a3185e32c2e613ae1ee55288f@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk