adding details on how preshow works
adding details on how preshow works

including a snippet of a preshow.json file. I had to hunt down an
example on github, so if this needs to be improved, feel free.

slambert/showoff,marrero984/showoff,slambert/showoff,puppetlabs/showoff,puppetlabs/showoff,slambert/showoff,marrero984/showoff,binford2k/showoff,puppetlabs/showoff,binford2k/showoff,puppetlabs/showoff,marrero984/showoff,marrero984/showoff,binford2k/showoff,binford2k/showoff,slambert/showoff