Straw to match the bales v1.0

The default straw windrow is a very pale colour and looks odd when contrasted against either the bales or the crop, this texture file addresses that issue, the straw matches the bales, so it looks the same comingout of the baler as it does going in, as well as the straw from the combine too. Also it looks less incongruous laying on the field. These files need adding manually, instructions in the readme file.