Update homebrew installation command and install git using homebrew.

This is the easiest way and works quite well. Takes care of installing
contrib too so we get credential osxkeychain helper and bash completion
and prompt. Git installer from git site would require more effort.
Feeling better about using homebrew as its proven real helpful with
postgres. We'll move the brew doctor path recommendation to dotfiles.
Output message when installing dotfiles and git.
Add brew install postgresql