Summary: this is largely just markdownified comments from `eden/fs/utils/PathFuncs.h`. I've been a bit confused on the differences lately and how they interact, so I read through that file and thought a markdown file would be helpful for future reference, since the file is reaching 2000 lines.
Reviewed By: fanzeyi
Differential Revision: D19434132
fbshipit-source-id: 0ec5551e9da0a3202fcc3efff52f9f6f48f99db4
