Documentation: id

[chrishaff]

I kept banging my head on the relational lookup stuff until I reviewed the code and found that the lookup column must be named lower case "id". Two thoughts:

1. Please add a note to the README.
2. To make this more flexible in cases where one may not have an easy option to mess with the csv please consider adding the name of the id column as a definition parameter (e.g. productcategories:n:productID).

I will be using your script alot, so I may just make the mods for #2 and send you a pull request, but first I have some deadlines...