Arduino Proto Shield Kit
Looking at the link, it seems this is intended as a prototyping board that is compatible with Arduino.   

If this is the case, then there are no need for schematics or assembly instructions as they do not know what you will want to use it for, that is you decide on it's function/circuit.
I suppose there could be some documentation with ideas to try, like a circuit cookbook, but they would not have to be associated particularly with this board.
This is similar to stripboard, or breadboard - the idea of these coming with schematics or assembly instructions doesn't make much sense.  

Once you have prototyped your circuit you could have a board made, and set the idea "in stone" (i.e. the board can only be used for that purpose and would need assembly instruction and schematic)