Clarify that default_bucket creates a bucket

Author: tuliocasagrande

src/sagemaker/session.py

@@ -355,6 +355,8 @@ def list_s3_files(self, bucket, key_prefix):
 
     def default_bucket(self):
         """Return the name of the default bucket to use in relevant Amazon SageMaker interactions.
+        
+        This function will create the s3 bucket if it does not exist.
 
         Returns:
             str: The name of the default bucket, which is of the form: