http://app2641.hatenablog.com/entry/2013/05/30/103529
を参考に以下で設定
スクリプトのインストール
mkdir -p /usr/local/git/contrib/completion/
cd /usr/local/git/contrib/completion/
wget https://raw.githubusercontent.com/git/git/master/contrib/completion/git-completion.bash
wget https://raw.githubusercontent.com/git/git/master/contrib/completion/git-prompt.sh
chmod 755 git-*
~/.bashrc
source /usr/local/git/contrib/completion/git-prompt.sh
source /usr/local/git/contrib/completion/git-completion.bash
GIT_PS1_SHOWDIRTYSTATE=true
export PS1='\[\033[1;32m\]\u@\h\[\033[00m\]:\[\033[1;34m\]\w\[\033[1;31m\]$(__git_ps1)\[\033[00m\]\$ '