further add to the index but you still haven't. You can
stage these changes by using linkgit:git-add.
-If exactly two paths are given, and at least one is untracked,
-compare the two files / directories. This behavior can be
+If exactly two paths are given and at least one points outside
+the current repository, 'git diff' will compare the two files /
+directories. This behavior can be forced by --no-index.
'git diff' [--options] --cached [<commit>] [--] [<path>...]::