Adding an installer tool

tools/install.sh

+if [ -d ~/.oh-my-zsh ]
+then
+  echo "You already have Oh My Zsh installed. You'll need to remove ~/.oh-my-zsh if you want to install"
+  exit
+else
+  echo "Cloning Oh My Zsh..."
+  /usr/bin/env git clone git://github.com/robbyrussell/oh-my-zsh.git ~/.oh-my-zsh
+fi
+
+echo "Looking for an existing zsh config..."
+if [ -f ~/.zshrc ]
+then
+  echo "Found ~/.zshrc. Backing up to ~/.zshrc.pre-oh-my-zsh";
+  cp ~/.zshrc ~/.zshrc.pre-oh-my-zsh;
+  rm ~/.zshrc;
+fi
+
+echo "Symlinking .zshrc to ~/.oh-my-zsh/"
+ln -s ~/.oh-my-zsh/zshrc ~/.zshrc
+
+echo "Time to change your default shell to zsh!"
+chsh -s /bin/zsh
+
+echo "Hooray! Oh My Zsh has been installed."