division_traced: add a comment about the 'id' parameter

my2to3/fixes/fix_division_trace.py

@@ -15,6 +15,9 @@ trace = create_table("division", "filename", "lineno", "id", "dividend_type", "d
 
 @register_tracing_function
 def division_traced(id, dividend, divisor):
+  # id is used to differentiate the divisions of the same line. It is not
+  # possible to obtain this information with inspect.currentframe() only.
+
   previous_frame = inspect.currentframe().f_back
 
   trace(