~/Projects> mkdir test123
~/Projects> cd test123
~/Projects/test123> mkdir extracted
~/Projects/test123> mkdir extracted/.git
~/Projects/test123> touch extracted/foo
~/Projects/test123> touch extracted/.git/config
~/Projects/test123> git init
Initialized empty Git repository in /home/chris/Projects/test123/.git/
[git:master] ~/Projects/test123> git add extracted/
[git:master] ~/Projects/test123> git status
On branch master

No commits yet

Changes to be committed:
  (use "git rm --cached <file>..." to unstage)

        new file:   extracted/foo

[git:master] ~/Projects/test123> git add extracted/.git/
error: Invalid path 'extracted/.git/config'
error: unable to add extracted/.git/config to index
fatal: adding files failed