Improve Note for PIKA

To reduce the amount of recorded data, PIKA summarizes per hardware thread metrics to the corresponding physical core. In terms of simultaneous multithreading (SMT), PIKA only provides performance data per physical core.

Could we add an example of the consequences, e. g. for CPU Usage? If SMT is 2 and CPU is 1, and we assume a single-threaded application runs, what does that mean for the CPU Usage plot?