add comments to clarify obscure xperf args
add comments to clarify obscure xperf args

MikeMarcin/UIforETW,modulexcite/UIforETW,OSVR/UIforETW,u-engine/UIforETW,MikeMarcin/UIforETW,modulexcite/UIforETW,MikeMarcin/UIforETW,google/UIforETW,google/UIforETW,OSVR/UIforETW,ariccio/UIforETW,google/UIforETW,OSVR/UIforETW,modulexcite/UIforETW,google/UIforETW,u-engine/UIforETW,ariccio/UIforETW,ariccio/UIforETW,mwinterb/UIforETW,mwinterb/UIforETW,u-engine/UIforETW,mwinterb/UIforETW,ariccio/UIforETW