added discription to setup_attribute function

tangostationcontrol/tangostationcontrol/clients/snmp_client.py

@@ -106,6 +106,10 @@ class SNMP_client(CommClient):
     def setup_attribute(self, annotation, attribute):
         """
         MANDATORY function: is used by the attribute wrapper to get read/write functions. must return the read and write functions
+
+        Gets called from inside the attributet wrapper. It is provided with the attribute_warpper itself
+        and the annotation provided when the attribute_wrapper was declared.
+        These parameters can be used to configure a valid read and write function as return values.
         """
 
         # process the annotation