Update prototype.md

materials/assignments/prototype.md

 # Paper Prototype
 
+**Approximate expected workload:** 5 hours
+
 Game ideas need to be presented somehow. Synopsis is a good start, but you need more tools. Paper prototyping is a really cost-effective tool for present for example your game mechanics. There are many things and reasons to present your game. 
 
 - Present your game to a publisher or investor