[utils] Document model-zoo

bob/ip/binseg/utils/model_zoo.py

@@ -32,6 +32,7 @@ modelurls = {
     "resnet50_SIN_IN": "https://bitbucket.org/robert_geirhos/texture-vs-shape-pretrained-models/raw/60b770e128fffcbd8562a3ab3546c1a735432d03/resnet50_finetune_60_epochs_lr_decay_after_30_start_resnet50_train_45_epochs_combined_IN_SF-ca06340c.pth.tar",
     "mobilenetv2": "https://dl.dropboxusercontent.com/s/4nie4ygivq04p8y/mobilenet_v2.pth.tar",
 }
+"""URLs of pre-trained models (backbones)"""
 
 
 def _download_url_to_file(url, dst, hash_prefix, progress):