#6524 Add doc for download size

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

@@ -919,7 +919,31 @@ The fully expanded example above (without environment variables) looks like this
   curl -H X-Dataverse-key:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx https://demo.dataverse.org/api/datasets/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 The size of published and unpublished files will be summed in the dataset specified.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 Because this deals with unpublished files the token supplied must have permission to view unpublished drafts.    
+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 Because this deals with unpublished files the token supplied must have permission to view unpublished drafts. 
+
+
+Get the size of Downloading all the files of a Dataset Version
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Shows the combined size in bytes of all the files available for download from version ``versionId`` of dataset ``id``. ::
+
+.. code-block:: bash
+
+  export API_TOKEN=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
+  export SERVER_URL=https://demo.dataverse.org
+  export ID=xxxxxx
+  export VERSIONID=x.x
+
+  curl -H X-Dataverse-key:$API_TOKEN $SERVER_URL/api/datasets/$ID/versions/$VERSIONID/downloadsize
+
+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/datasets/xxxxxx/versions/x.x/downloadsize
+
+The size of all files available for download will be returned. 
+If :draft is passed as versionId the token supplied must have permission to view unpublished drafts. A token is not required for published datasets. Also restricted files will be included in this total regardless of whether the user has access to download the restricted file(s).
 
 Submit a Dataset for Review
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -1095,7 +1119,7 @@ Accessing (downloading) files
 
   Example: Getting the file whose DOI is *10.5072/FK2/J8SJZB* ::
 
-    GET http://$SERVER/api/access/datafile/:persistentId/?persistentId=doi:10.5072/FK2/J8SJZB
+    GET http://$SERVER/api/access/datafile/:persistentId/?persistentId=doi:10.5072/FK2/J8SJZB    
 
 
 Restrict Files