message: Update FREEBSD_HOWTO.txt
diff: -see LINUX_HOWTO.txt (but use gmake instead of make to build).
  +Building:
  +$ gmake
  +
  +Runtime requirements:
  +* the cpuctl(4) driver needs to be loaded
  +
  +PCM is also available as a port maintained by The FreeBSD Project (sysutils/intel-pcm).
  