update doc for transfer_learning (#3473)

PaddleCV/PaddleDetection/docs/TRANSFER_LEARNING.md

@@ -18,7 +18,7 @@ python -u tools/train.py -c configs/faster_rcnn_r50_1x.yml \
 
 * Note:
 
-1. The path in pretrain\_weights is the open-source model link of faster RCNN from COCO dataset
+1. The path in pretrain\_weights is the open-source model link of faster RCNN from COCO dataset. For full models link, please refer to [MODEL_ZOO](MODEL_ZOO.md)
 2. The parameter fields are set in finetune\_exclude\_pretrained\_params. If the name of parameter matches field (wildcard matching), the parameter will be ignored in loading.
 
 If users want to fine-tune by own dataet, and remain the model construction, need to ignore the parameters related to the number of classes. PaddleDetection lists ignored parameter fields corresponding to different model type. The table is shown below: </br>

PaddleCV/PaddleDetection/docs/TRANSFER_LEARNING_cn.md

@@ -18,7 +18,7 @@ python -u tools/train.py -c configs/faster_rcnn_r50_1x.yml \
 
 * 说明：
 
-1. pretrain\_weights的路径为COCO数据集上开源的faster RCNN模型链接
+1. pretrain\_weights的路径为COCO数据集上开源的faster RCNN模型链接，完整模型链接可参考[MODEL_ZOO](MODEL_ZOO_cn.md)
 2. finetune\_exclude\_pretrained\_params中设置参数字段，如果参数名能够匹配以上参数字段（通配符匹配方式），则在模型加载时忽略该参数。
 
 如果用户需要利用自己的数据进行finetune，模型结构不变，只需要忽略与类别数相关的参数。PaddleDetection给出了不同模型类型所对应的忽略参数字段。如下表所示：</br>