Add explanatory comment for harvest_element_tree usage

Author: c00kiemon5ter

src/saml2/saml.py

@@ -1093,6 +1093,7 @@ def __init__(self,
         self.name_format = name_format
         self.friendly_name = friendly_name
 
+    # when consuming such elements, default to NAME_FORMAT_UNSPECIFIED as NameFormat
     def harvest_element_tree(self, tree):
         tree.attrib.setdefault('NameFormat', NAME_FORMAT_UNSPECIFIED)
         SamlBase.harvest_element_tree(self, tree)