Sometimes, it's useful to create a branch that doesn't contain the main files, for example, to store other related files to the project, such as, media files, PSD, etc.
This procedure was taken from gh-pages
http://pages.github.com/
$ cd /path/to/repo
$ git symbolic-ref HEAD refs/heads/<branch_name>
$ rm .git/index
$ git clean -fdx
Now your directory is clean, you can add whatever you want to add to it.
$ echo "Hello! This is another branch that doesn't have the main files" > index.html
$ git add .
$ git commit -a -m "Committing into the media branch"
Once done, you can verify by:
$ git branch
Now you can push it to remote branch.
$ git push origin <branch_name>