Added partial support for private files

*   if dotfiles are shared by git, it will ignore
    all files under dotfiles/git-universe/private

*   if you use other sharing mechanism, you need
    to exclude these files other way

.gitignore

 *~
 .*.swp
 .netrwhist
+*/git-universe/private/*

dotfiles/git-universe/setup

 printf "    path = $tilde/.git-universe/gitconfig-before\n" >> ~/.gitconfig
 printf "    path = $tilde/.git-universe/host/$host.gitconfig\n" >> ~/.gitconfig
 printf "    path = $tilde/.git-universe/user/$user.gitconfig\n" >> ~/.gitconfig
+printf "    path = $tilde/.git-universe/private/gitconfig\n" >> ~/.gitconfig
 printf "    path = $tilde/.git-universe/gitconfig-after\n" >> ~/.gitconfig