added cmake_prefix_path access for building cyclus in cnerg's cae space
updated the description, because the information about optional parameters and parameters in general comes with the help description. it now points people to the cyclus website if additional information is needed.
more than 80 chars in my haste.
Merge pull request #516 from gidden/setup-cnerg

added cmake_prefix_path access for building cyclus in cnerg's cae space