Update project description, reorganize Windows instructions
Update project description, reorganize Windows instructions

* Updated the project description to be more current, and describe what the
  project is.
* Reorganized the windows instructions to be clearer, in my opinion.
* Added FreeGlut as an optional dependency.
* Spellchecked

simquest/opensurgsim,simquest/opensurgsim,simquest/opensurgsim,simquest/opensurgsim