add def about default

fixed_f1.py

@@ -24,7 +24,7 @@ _CITATION = """
 _INPUTS = """
 'average': This parameter is required for multiclass/multilabel targets. 
 If None, the scores for each class are returned. Otherwise, this determines the type of averaging performed on the data. 
-Options include: {‘micro’, ‘macro’, ‘samples’, ‘weighted’, ‘binary’} or None.
+Options include: {‘micro’, ‘macro’, ‘samples’, ‘weighted’, ‘binary’} or `None`. The default is `binary`.
 """
 
 # could in principle subclass the F1 Metric, but ideally we can work the fix into HF evaluate's main F1 class to maintain SOLID code