docs: add "Merge Datasets" link to the top of dataset_management

PR Closed: #994

Author: zhen.chen

docs/source/features/dataset_management.rst

@@ -9,6 +9,7 @@ This topic describes dataset management, including:
 - :ref:`features/dataset_management:Read Dataset`
 - :ref:`features/dataset_management:Update Dataset`
 - :ref:`features/dataset_management:Move and Copy`
+- :ref:`features/dataset_management:Merge Datasets`
 
 
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