update gluonbook index

chapter_appendix/gluonbook.md

@@ -22,6 +22,7 @@
 | `load_data_fashion_mnist`|[深度卷积神经网络（AlexNet）](../chapter_convolutional-neural-networks/alexnet.md)|
 |`load_data_jay_lyrics`|[语言模型数据集（周杰伦专辑歌词）](../chapter_recurrent-neural-networks/lang-model-dataset.md)|
 | `load_data_pikachu`|[物体检测数据集（皮卡丘）](../chapter_computer-vision/object-detection-dataset.md)|
+| `mkdir_if_not_exist`|[实战Kaggle比赛：图像分类（CIFAR-10）](../chapter_computer-vision/kaggle-gluon-cifar10.md)|
 | `plt`|[线性回归的从零开始实现](../chapter_deep-learning-basics/linear-regression-scratch.md)|
 | `predict_rnn`|[循环神经网络的从零开始实现](../chapter_recurrent-neural-networks/rnn-scratch.md)|
 | `predict_rnn_gluon`|[循环神经网络的Gluon实现](../chapter_recurrent-neural-networks/rnn-gluon.md)|