document that cf-173.yml doesn't work with these docs

I got tripped up trying to run through this tutorial on the latest
release.  Too much has changed:

 - the release.tgz has doubled in size from 1.3G to 2.5G and won't fit,
   exploded, on the microBOSH instance's /var/vcap/data volume
 - cf-173 doesn't define the health_manager_next template, required by
   the sample cf.yml.erb file
Merge pull request #26 from philandstuff/document-173-doesnt-work

document that cf-173.yml doesn't work with these docs