added some comments

brian_polling_manager/sensu.py

@@ -159,14 +159,17 @@ class AbstractCheck(object):
 
     @property
     def name(self):
+        # overridden implementation must return a string
         assert False, 'property StandardCheck.name must be overridden'
 
     @property
     def command(self):
+        # overridden implementation must return a string
         assert False, 'property StandardCheck.command must be overridden'
 
     @property
     def proxy_entity_name(self):
+        # overridden implementation must return a string
         assert False, \
             'property StandardCheck.proxy_entity_name must be overridden'