#6524 add doc for dataset storage size

doc/sphinx-guides/source/api/native-api.rst

@@ -898,6 +898,28 @@ In practice, you only need one the ``dataset_id`` or the ``persistentId``. The e
     print '-' * 40
     print r.json()
     print r.status_code
+    
+Report the data (file) size of a Dataset
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Shows the combined size in bytes of all the files uploaded into the dataset ``id``. ::
+
+.. code-block:: bash
+
+  export API_TOKEN=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
+  export SERVER_URL=https://demo.dataverse.org
+  export ID=xxxxxx
+
+  curl -H X-Dataverse-key:$API_TOKEN $SERVER_URL/api/datasets/$ID/storagesize
+
+The fully expanded example above (without environment variables) looks like this:
+
+.. code-block:: bash
+
+  curl -H X-Dataverse-key:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx https://demo.dataverse.org/api/dataverses/xxxxxx/storagesize
+
+The size of published and unpublished files will be summed in the dataset specified. 
+By default, only the archival files are counted - i.e., the files uploaded by users (plus the tab-delimited versions generated for tabular data files on ingest). If the optional argument ``includeCached=true`` is specified, the API will also add the sizes of all the extra files generated and cached by Dataverse - the resized thumbnail versions for image files, the metadata exports for published datasets, etc. Because this deals with unpublished files the token supplied must have permission to view unpublished drafts.    
 
 Submit a Dataset for Review
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~