some explanation on addLayer functionality

Author: Shouqyan

Diff for: README.md

@@ -32,6 +32,7 @@ To ensure uniqueness, we want to add various features and multiple options for e
 To start, copy the layers/features and their images in a flat hierarchy at a directory of your choice (by default we expect them in `./input/`). The features should contain options for each rarity that is provided via the config file.
 
 After adding the `layers`, adjust them accordingly in the `config.js` by providing the directory path, positioning and sizes.
+Use the existing `addLayers` calls as guidance for how to add layers. This can either only use the name of the layer and will use default positioning (x=0, y=0) and sizes (width=configured width, height=configure height), or positioning and sizes can be provided for more flexibility.
 
 ### Allowing different rarities for certain rarity/layer combinations
 It is possible to provide a percentage at which e.g. a rare item would contain a rare vs. common part in a given layer. This can be done via the `addRarityPercentForLayer` that can be found in the `config.js` as well. 

Diff for: input/config.js

@@ -142,7 +142,7 @@ let rarityWeights = [
 // for each layer, call 'addLayer' with the id and optionally the positioning and size
 // the id would be the name of the folder in your input directory, e.g. 'ball' for ./input/ball
 const layers = [
-  addLayer('ball'),
+  addLayer('ball', { x: 0, y: 0 }, { width: width, height: height }),
   addLayer('eye color'),
   addLayer('iris'),
   addLayer('shine'),