Add description of structure modeling and Gibbs samlping therein.

I have sort of just put that in there.  It could use some editing, no
doubt.
Merge branch 'master' of https://github.com/eriqande/flock-comment

I am merging in Patrick's additions.  Seems pretty straightforward.
Delete flock-comment-main.synctex.gz

This file was under version control for some reason.  It got deleted,
I think, today when I upgraded to the new version of TeXShop.  At any
rate, it is not necessary to have it under version control.  I've added
it to .gitignore, too.