doc: add tuning step to doc (#2509)

Co-authored-by: Ahsan Khan <[email protected]>
Co-authored-by: apogupta2018 <[email protected]>

Author: 3 people

doc/workflows/pipelines/sagemaker.workflow.pipelines.rst

@@ -115,6 +115,8 @@ Steps
 
 .. autoclass:: sagemaker.workflow.steps.ProcessingStep
 
+.. autoclass:: sagemaker.workflow.steps.TuningStep
+
 Utilities
 ---------