Add a better explanation of "weird things" in WebGLRenderer

src/renderers/WebGLRenderer.js

@@ -1770,7 +1770,7 @@ function WebGLRenderer( parameters ) {
 
 		// skinning uniforms must be set even if material didn't change
 		// auto-setting of texture unit for bone texture must go before other textures
-		// not sure why, but otherwise weird things happen
+		// otherwise textures used for skinning can take over texture units reserved for other material textures
 
 		if ( material.skinning ) {