[Example] Add docstring for test optimizer and test score

cpp-package/example/test_optimizer.cpp

@@ -15,6 +15,10 @@
  * KIND, either express or implied.  See the License for the
  * specific language governing permissions and limitations
  * under the License.
+ * 
+ * The file is used for testing if the optimizer could be created more than 1.
+ * By running: build/test_optimizer
+ * It return 0(means no error) if it succeed otherwise 1(error).
  */
 #include "mxnet-cpp/MxNetCpp.h"
 

cpp-package/example/test_score.cpp

@@ -19,6 +19,11 @@
 
 /*!
  * Xin Li [email protected]
+ * The file is used for testing if the score(accurary) we get
+ * is better than the threshold we set using mlp model.
+ * By running: build/test_score 0.75
+ * 0.75 here means the threshold score
+ * It return 0 if we can achieve higher score than threshold, otherwise 1
  */
 #include <chrono>
 #include "utils.h"