[cherry pick] fix README for yolov3 (#931)

* fix README for yolov3

* add NOTE

README.md

@@ -46,13 +46,15 @@
 | Cascade Mask-RCNN  | ✓      |                             ✗ | ✗          | ✓     | ✗         |  ✗     |  ✗      |
 | Libra R-CNN        | ✗      |                             ✓ | ✗          | ✗     | ✗         |  ✗     |  ✗      |
 | RetinaNet          | ✓      |                             ✗ | ✓          | ✗     | ✗         |  ✗     |  ✗      |
-| YOLOv3             | ✓      |                             ✗ | ✗          | ✗     | ✓         |  ✗     |  ✗      |
+| YOLOv3             | ✓      |                             ✓ | ✗          | ✗     | ✓         |  ✗     |  ✗      |
 | SSD                | ✗      |                             ✗ | ✗          | ✗     | ✓         |  ✗     |  ✗      |
 | BlazeFace          | ✗      |                             ✗ | ✗          | ✗     | ✗         |  ✗     |  ✗      |
 | Faceboxes          | ✗      |                             ✗ | ✗          | ✗     | ✗         |  ✗     |  ✗      |
 
 <a name="vd">[1]</a> [ResNet-vd](https://arxiv.org/pdf/1812.01187) 模型预测速度基本不变的情况下提高了精度。
 
+**说明：** ✓ 为[模型库](docs/MODEL_ZOO_cn.md)中提供了对应配置文件和预训练模型，✗ 为未提供参考配置，但一般都支持。
+
 更多的模型:
 
 - EfficientDet

README_en.md

@@ -60,13 +60,15 @@ Supported Architectures:
 | Cascade Mask-RCNN   |   ✓    |                             ✗ |     ✗      |   ✓   |     ✗     |   ✗    |  ✗      |
 | Libra R-CNN         |   ✗    |                             ✓ |     ✗      |   ✗   |     ✗     |   ✗    |  ✗      |
 | RetinaNet           |   ✓    |                             ✗ |     ✗      |   ✗   |     ✗     |   ✗    |  ✗      |
-| YOLOv3              |   ✓    |                             ✗ |     ✗      |   ✗   |     ✓     |   ✗    |  ✗      |
+| YOLOv3              |   ✓    |                             ✓ |     ✗      |   ✗   |     ✓     |   ✗    |  ✗      |
 | SSD                 |   ✗    |                             ✗ |     ✗      |   ✗   |     ✓     |   ✗    |  ✗      |
 | BlazeFace           |   ✗    |                             ✗ |     ✗      |   ✗   |     ✗     |   ✗    |  ✗      |
 | Faceboxes           |   ✗    |                             ✗ |     ✗      |   ✗   |     ✗     |   ✗    |  ✗      |
 
 <a name="vd">[1]</a> [ResNet-vd](https://arxiv.org/pdf/1812.01187) models offer much improved accuracy with negligible performance cost.
 
+**NOTE:** ✓ for config file and pretrain model provided in [Model Zoo](docs/MODEL_ZOO.md), ✗ for not provided but is supported generally.
+
 More models:
 
 - EfficientDet