Add notes on zsh, oh-my-zsh, rbenv, ruby-build to README and depreciate adjust-path.el.
Set $SHELL as well as $ESHELL

rbenv, etc. rely on $SHELL to be properly configured
Merge branch 'master' into emacs_24_and_packages

* master:
  Set $SHELL as well as $ESHELL
  Add notes on zsh, oh-my-zsh, rbenv, ruby-build to README and depreciate adjust-path.el.