Added the documentation for Google Checkout.
Added the documentation for Google Checkout.

digideskio/merchant,SimpleTax/merchant,agiliq/merchant,digideskio/merchant,mjrulesamrat/merchant,mjrulesamrat/merchant,spookylukey/merchant,biddyweb/merchant,spookylukey/merchant,SimpleTax/merchant,agiliq/merchant,biddyweb/merchant