Added newly-rewritten document describing OSGB to HMRC file transfer specifics.
Added newly-rewritten document describing OSGB to HMRC file transfer specifics.

andywhardy/address-reputation-ingester,andywhardy/address-reputation-ingester,andywhardy/address-reputation-ingester,andywhardy/address-reputation-ingester,andywhardy/address-reputation-ingester