allow projectile-project-root to find the root for symlinked files

This covers the case where you have a git repo `~/configs` (for dotfiles etc.), and the subdir `emacs` of that repo is symlinked to `~/.emacs.d`

projectile-project-root in a buffer visiting `~/.emacs.d/init.el` will find the root at `~/configs`.

Also includes an unrelated docstring fix.