Added instructions to run horizontal secure XGBoost in simulator (#2890)

* Added simulator instructions for tenseal context

* Fixed reference

* Fixing target

* Renamed provisioning target to xgb_provisioning

---------

Co-authored-by: Yuan-Ting Hsieh (謝沅廷) <[email protected]>

docs/user_guide/federated_xgboost/secure_xgboost_user_guide.rst

@@ -78,6 +78,8 @@ The following docker image is recommended for GPU training:
 
 Most Linux distributions are supported, as long as they have a recent glibc. The oldest glibc version tested is 2.35. Systems with older glibc may run into issues.
 
+.. _xgb_provisioning:
+
 NVFlare Provisioning
 --------------------
 For horizontal secure training, the NVFlare system must be provisioned with homomorphic encryption context. The HEBuilder in ``project.yml`` is used to achieve this.
@@ -190,7 +192,19 @@ The plugin setup is the same as vertical secure.
 
 This mode requires the tenseal package for all plugins.
 The provisioning of NVFlare systems must include tenseal context.
-See :ref:`provisioning` for details.
+See :ref:`xgb_provisioning` for details.
+
+For simulator, the tenseal context generated by provisioning needs to be copied to the startup folder,
+
+``simulator_workspace/startup/client_context.tenseal``
+
+For example,
+
+.. code-block:: bash
+
+    nvflare provision -p secure_project.yml -w /tmp/poc_workspace
+    mkdir -p /tmp/simulator_workspace/startup
+    cp /tmp/poc_workspace/example_project/prod_00/site-1/startup/client_context.tenseal /tmp/simulator_workspace/startup
 
 
 Job Configuration