code: private PBXObjectRef addDocumentationGroup(final Map objects, final String sourceTree) {
      final List productsList = new ArrayList();
      final PBXObjectRef products = createPBXGroup("Documentation", sourceTree, productsList);
      objects.put(products.getID(), products.getProperties());
      return products;
    }
docs: Add documentation group to map of objects.
  
  @param objects
  object map.
  @param sourceTree
  source tree description.
  @return documentation group.