doc: update docstring

Author: msto

fgpyo/util/metric.py

@@ -367,8 +367,8 @@ def is_attrs_instance(metric: Metric) -> TypeGuard[inspect.AttrsInstance]:
     """
     Test if the given metric is an attr.s instance.
 
-    NB: `attr.has` does not provide a type guard, which we need to use other `attr` methods such as
-    `asdict()`, so we implement one here.
+    NB: `attr.has` provides a type guard, but only on the class object - we want to narrow the type
+    of the metric instance, so we implement a guard here.
 
     Args:
         metric: An instance of a Metric.