Returns the strikerate for a single product. A strikerate is the number of sales that contain at least one item from the department as a percentage of all sales. See department.strikerate pinboard for deeper explanation.
= Pinboard("product.strikerate", Product-Number, Location, Start Date, End Date)
=Pinboard("product.strikerate", 6011,,"1 may 2015", "1-jun-2015")
Return the strikerate in the month of May 2015 for product 6011