Merge pull request #29 from Crazy-Chick/main

add checkout in README.md

Author: YuxianMeng

README.md

@@ -127,7 +127,10 @@ then move them under `preprocessed_data_dir/`
 
 Since file `train.objects.mmap` is too large(100G+), 
 we splitted it to many small pieces like `train.objects.mmap.split*`, 
-and you need another step to merge all those files together: `cat train.objects.mmap.split* >train.objects.mmap`
+and you need another step to merge all those files together: `cat train.objects.mmap.split* >train.objects.mmap`  
+
+##### Checkout
+Each of files has a hash value by command `md5sum fileName`. You can get it from [here](https://drive.google.com/file/d/1COXpOvw6pCjTXppb86JmSDj7iGx6BOnO/view?usp=sharing) and we suggest you check each file's hash value before training.
 
 ##### (Optional) Extract features on your own
 If you want to extract some feature on your own, or you'd like to know details of extracting visual features,