Creates a simple overlay for the current buffer that shows non-staged git chunks.
Lines around additions/deletions are shown blue, additions in green, deletions in red.
Just copy it somewhere in your load-path, or add the directory containing the git-overlay.el file with (add-to-list 'load-path "/path/to/repo/")
Then just (require 'git-overlay) and do M-x git-overlay in a buffer with a file from a git repository open.
Calling git-overlay twice will toggle the overlays on and off. If you change the buffer while the git overlays are shown they will disappear.