Small fixes for doc.

doc/tutorials/saving_model.rst

@@ -194,4 +194,4 @@ Right now using the JSON format incurs longer serialisation time, we have been w
 optimizing the JSON implementation to close the gap between binary format and JSON format.
 You can track the progress in `#5046 <https://github.com/dmlc/xgboost/pull/5046>`_.
 Another important item for JSON format support is a stable and documented `schema
-<https://json-schema.org/>`_, based on which one can easily resued the saved model.
+<https://json-schema.org/>`_, based on which one can easily reuse the saved model.

include/xgboost/c_api.h

@@ -489,6 +489,7 @@ XGB_DLL int XGBoosterSaveRabitCheckpoint(BoosterHandle handle);
  * \param out_str A valid pointer an array of characters.  The characters array is
  *                allocated and managed by XGBoost, while pointer to that array needs to
  *                be managed by caller.
+ * \return 0 when success, -1 when failure happens
  */
 XGB_DLL int XGBoosterSaveJsonParameters(BoosterHandle handle,
                                         bst_ulong *out_len,
@@ -497,6 +498,7 @@ XGB_DLL int XGBoosterSaveJsonParameters(BoosterHandle handle,
  * \brief Load XGBoost's internal configuration from a JSON document.
  * \param handle handle to Booster object.
  * \param json_parameters string representation of a JSON document.
+ * \return 0 when success, -1 when failure happens
  */
 XGB_DLL int XGBoosterLoadJsonParameters(BoosterHandle handle,
                                         char const* json_parameters);