Add intern job posting

@gidden @rwcarlsen @katyhuff 

I'm planning to expand the search for Cyclus help to include a "Research Intern" - basically a post-doc like position for someone without a PhD.  My draft of the position description, scaled back from the research parts of the Post-Doc announcement, is in this pull request.  It is aimed more at a computer scientist than an engineer (perhaps).

Please consider the following questions in your feedback:

* is an MS important/necessary?  (I am not sure what title I can have for a position that is not a MS, but can investigate)
* are their any skills missing?
* other thoughts?