[TinyCLIP] Update PRETRAINING.md

Author: wkcn

TinyCLIP/docs/PRETRAINING.md

@@ -4,6 +4,8 @@ In this document, we introduce ***auto weight inheritance*** and ***manual weigh
 
 :star: **[Notice]** Please replace the training data loader with the one loading LAION-400M or YFCC-15M.
 
+Reference: [OpenCLIP Data](https://github.com/mlfoundations/open_clip?tab=readme-ov-file#data)
+
 ###  Auto weight inheritance training
 In this part, we compress OpenCLIP ViT-B/32 to 25% of origin size using three stages, where the model is compressed from 100% to 75%, from 75% to 50% and from 50% to 25% in the three stages, respectively.