Update README.md

Described the levels Michael & I discussed on Thursday and organized this by level...obviously some assets can be re-used in more than one space but I figured these 2 lists would start to get really long and it would be good to categorize what's going where so that people doing models can take a look at the right level sketch Blender file/have an idea which area they are creating the model for since each place might have a slightly different look etc