You are confused about something. 401(k)s and IRAs are different types of retirement accounts, and QCDs are only permitted to be made from an IRA, not from a 401(k). If the Form 1099-R provided by the payer has the IRA/SEP/SIMPLE box marked (which seems to be the case if you entered the form correctly into TurboTax), the distribution is from an IRA and is reportable as a QCD. No other documentation is required with your tax return beyond the "QCD" notation on line 4b of Form 1040.
If the distribution was indeed from a 401(k) and the Form 1099-R provided by the payer does not have the IRA/SEP/SIMPLE box marked (contrary to the way you seems to have in marked on TurboTax's 1099-R form), the charitable contribution is not excludible from line 5b Form 1040 and your AGI, and your charitable contribution must be reported on Schedule A the same as you would a charitable contribution not made from some other source of funds.
