Added install instructions for Homebrew users

Mac OS X users of Homebrew can install gcc-arm-embedded from a Formula
Merge pull request #494 from bfoz/patch-1

Added install instructions for Homebrew users
update firnware.bin and checksum
Merge branch 'edge' of github.com:Smoothieware/Smoothieware into edge
Update README.creole
Merge remote-tracking branch 'upstream/edge' into edge