README: tweak donations, sponsors.
README: tweak donations, sponsors.

Move "Donations" below "Contributing" so people see it more and remove CommsWorld who we no longer use.
EricFromCanada/brew,vitorgalvao/brew,claui/brew,vitorgalvao/brew,Homebrew/brew,claui/brew,nandub/brew,sjackman/homebrew,sjackman/homebrew,MikeMcQuaid/brew,mahori/brew,EricFromCanada/brew,JCount/brew,vitorgalvao/brew,reitermarkus/brew,Homebrew/brew,mahori/brew,nandub/brew,JCount/brew,JCount/brew,konqui/brew,reitermarkus/brew,mahori/brew,MikeMcQuaid/brew,Homebrew/brew,sjackman/homebrew,claui/brew,EricFromCanada/brew,vitorgalvao/brew,konqui/brew,MikeMcQuaid/brew,claui/brew,Homebrew/brew,JCount/brew,EricFromCanada/brew,reitermarkus/brew,MikeMcQuaid/brew,mahori/brew,nandub/brew,konqui/brew,konqui/brew,sjackman/homebrew,nandub/brew,reitermarkus/brew