Add section on optimisations to README
Add section on optimisations to README

xlqian/benchmark,fuchsia-mirror/third_party-benchmark,codygray/benchmark,ntx-/benchmark,chemhack/benchmark,google/benchmark,disconnect3d/benchmark,mockingbirdnest/benchmark,xlqian/benchmark,codygray/benchmark,codygray/benchmark,fuchsia-mirror/third_party-benchmark,codygray/benchmark,ntx-/benchmark,nickhutchinson/benchmark-cxx03,nickhutchinson/benchmark-cxx03,nickhutchinson/benchmark,everbase/benchmark,google/benchmark,everbase/benchmark,LepelTsmok/benchmark,ntx-/benchmark,chemhack/benchmark,nickhutchinson/benchmark,xlqian/benchmark,efcs/benchmark,efcs/benchmark,chemhack/benchmark,efcs/benchmark,everbase/benchmark,disconnect3d/benchmark,fuchsia-mirror/third_party-benchmark,xlqian/benchmark,efcs/benchmark,LepelTsmok/benchmark,fuchsia-mirror/third_party-benchmark,nickhutchinson/benchmark,mockingbirdnest/benchmark,nickhutchinson/benchmark-cxx03,LepelTsmok/benchmark,nickhutchinson/benchmark-cxx03,ntx-/benchmark,chemhack/benchmark,disconnect3d/benchmark,LepelTsmok/benchmark,mockingbirdnest/benchmark,everbase/benchmark,nickhutchinson/benchmark,disconnect3d/benchmark,google/benchmark,mockingbirdnest/benchmark