remove comment with link to Django snippet 1040

* the snippet was removed since it's now obsolete - the new Django Meta
 o\Options API has new methods, _eg_: `get_fields()`, to get fields, to
 filter out parent, autogenerated and reverse fields from a model
* add new comment that links to new Django Meta Options API

carousel/contrib/readers.py

@@ -17,7 +17,12 @@
 
 def copy_model_instance(obj):
     """
-    https://djangosnippets.org/snippets/1040/
+    Copy Django model instance as a dictionary excluding automatically created
+    fields like an auto-generated sequence as a primary key or an auto-created
+    many-to-one reverse relation.
+
+    :param obj: Django model object
+    :return: copy of model instance as dictionary
     """
     meta = getattr(obj, '_meta')  # make pycharm happy
     # dictionary of model values excluding auto created and related fields