[git] add alias to get current branch name
[git] add alias to get current branch name

This is useful for scripting

ptgamr/dotfiles,damca/dotfiles-ubuntu,joeandrews/dotfiles,jacobxk/dotfiles-1,SlyDen/dotfiles,pekosi/dotfiles,abhisood/dotfiles,Jooho/dotfiles_mac,OctavianRotari/dotfiles,ptgamr/dotfiles,neutrinog/dotfiles,dyong0/dotfiles,Jooho/dotfiles_mac,fieteboerner/dotfiles,jbargu/dotfiles,Reesi82/dotfiles,Boukefalos/dotfiles,nicknisi/dotfiles,OctavianRotari/dotfiles,fieteboerner/dotfiles,zhenglaizhang/dotfiles-1,patnolanireland/dotfiles,jbargu/dotfiles,jacobxk/dotfiles-1,fieteboerner/dotfiles,damca/dotfiles-ubuntu,paulhirschi/dotfiles,nicknisi/dotfiles,NerdPad/dotfiles,bbtb1982/dotfiles,zhenglaizhang/dotfiles-1,gblock0/dotfiles_unstable,pekosi/dotfiles,patnolanireland/dotfiles,nicknisi/dotfiles,bbtb1982/dotfiles