OpenMC: finalize installation

Now I think everyone has OpenMC downloaded. The next step is to get the file "cross_sections.xml" and the folder "nndc_hdf5". On Canvas, I've uploaded a step-by-step guide "OpenMC_cross_sectionxml_todo" on how to get this set up properly. Please try to follow this guide, and tell me if you encounter any challenges.

Also, go through the exercise "Modelling a Pin Cell", and understand what happens.

On Thursday next week, we'll get started on the exercises. You'll be given a "startup script", so you don't have to build the reactor from scratch.