Added boxen upgrade instructions
update Puppetfile homebrew version
Merge pull request #590 from jakecraige/master

update Puppetfile homebrew version
Added more detailed update process
Moved Upgrading instructions to FAQ
fixed spelling error
Update README.md

Other boxem fixed.
Merge pull request #587 from nbmorgan/master

Added boxen upgrade instructions
Upgrade puppet-git to 2.3.1

Closes #598
Merge remote-tracking branch 'upstream/master'