"git add" doesn't work in Power Shell

``` bash
C:\GitHub\github-for-developers-sept-2015 [master +0 ~2 -0]> git status
# On branch master
# Your branch is behind 'origin/master' by 27 commits, and can be fast-forwarded
.
# (use "git pull" to update your local branch)
#
# Changes not staged for commit:
# (use "git add ..." to update what will be committed)
# (use "git checkout -- ..." to discard changes in working directory)
#
# modified: README.md
# modified: another file
#
no changes added to commit (use "git add" and/or "git commit -a")
C:\GitHub\github-for-developers-sept-2015 [master +0 ~2 -0]> git add README.md
C:\GitHub\github-for-developers-sept-2015 [master +0 ~2 -0]> git add '.\Another
file'
C:\GitHub\github-for-developers-sept-2015 [master +0 ~2 -0]> git status
# On branch master
# Your branch is behind 'origin/master' by 27 commits, and can be fast-forwarded
.
# (use "git pull" to update your local branch)
#
# Changes not staged for commit:
# (use "git add ..." to update what will be committed)
# (use "git checkout -- ..." to discard changes in working directory)
#
# modified: README.md
# modified: another file
#
no changes added to commit (use "git add" and/or "git commit -a")
C:\GitHub\github-for-developers-sept-2015 [master +0 ~2 -0]>
```