message: add a note for windows builds
diff: @@ -154,6 +154,9 @@ build-mpi: $(MPI_TARGETS)
  .PHONY: build
  build: bin/stanc$(EXE) bin/stansummary$(EXE) bin/print$(EXE) bin/diagnose$(EXE) $(LIBSUNDIALS) $(MPI_TARGETS) $(TBB_TARGETS) $(CMDSTAN_MAIN_O)
  @echo ''
  + @if [ "$(OS)" == "Windows_NT" ]; then \
  + echo 'Please add $(TBB_ABSOLUTE_PATH)/lib to your PATH variable.';\
  + fi
  @echo '--- CmdStan v$(CMDSTAN_VERSION) built ---'
  ifeq ($(CXX_TYPE),clang)
  