DOC: Add explanation on collection_mode to docstring

src/caoscrawler/converters/converters.py

@@ -179,7 +179,10 @@ value: Union[dict, str, list]
     ``collection_mode``. The returned tuple is directly created from
     the corresponding values if they are given; ``unit`` defaults to
     None and ``collection_mode`` is determined from ``value`` as
-    explained for the str case above.
+    explained for the str case above, i.e.,
+    - if it starts with '+', collection mode is "list",
+    - in case of '*', collection mode is "multiproperty",
+    - and everything else is "single".
   - If *list*, each element is checked for replacement and the
     resulting list will be used as (list) value for the property