Improve docstring

pysr/sr.py

@@ -205,7 +205,9 @@ class PySRRegressor(MultiOutputMixin, RegressorMixin, BaseEstimator):
     Parameters
     ----------
     model_selection : str, default="best"
-        Model selection criterion. Can be 'accuracy', 'best', or 'score'.
+        Model selection criterion when selecting a final expression from
+        the list of best expression at each complexity.
+        Can be 'accuracy', 'best', or 'score'.
         - `"accuracy"` selects the candidate model with the lowest loss
           (highest accuracy).
         - `"score"` selects the candidate model with the highest score.