add xgboost version

docs/user_guide/federated_xgboost/secure_xgboost_user_guide.rst

@@ -37,7 +37,7 @@ It requires XGBoost 2.2 or above, which can be installed using this command,
 
 .. code-block:: bash
 
-	pip install xgboost
+	pip install "xgboost>=2.2"
 
 ``TenSEAL`` package is needed for horizontal secure training,