documentation: Mark baseline as optional in KernelSHAP.

Author: larroy

src/sagemaker/clarify.py

@@ -305,10 +305,11 @@ def __init__(
         """Initializes config for SHAP.
 
         Args:
-            baseline (str or list): A list of rows (at least one) or S3 object URI to be used as
+            baseline (None or str or list): None or S3 object Uri or A list of rows (at least one) to be used as
                 the baseline dataset in the Kernel SHAP algorithm. The format should be the same
                 as the dataset format. Each row should contain only the feature columns/values
-                and omit the label column/values.
+                and omit the label column/values. If None a baseline will be calculated automatically by using K-means
+                or K-prototypes in the input dataset.
             num_samples (int): Number of samples to be used in the Kernel SHAP algorithm.
                 This number determines the size of the generated synthetic dataset to compute the
                 SHAP values.