Makefile: Adds install-brew to install latest from homebrew.
Makefile: Adds install-brew to install latest from homebrew.

- install-brew complements install-dev.
- These two commands together allow you to switch your locally installed
  sous between your own personal dev build and the latest homebrew release
  from opentable/public/sous.
- These commands are both for developers only, ordinary users should just use
  the homebrew commands directly, or else install sous manually from the release
  tarballs.

opentable/sous,samsalisbury/sous,samsalisbury/sous,opentable/sous,opentable/sous,opentable/sous,samsalisbury/sous,samsalisbury/sous,opentable/sous,samsalisbury/sous