Update dataset docs for HTC/DetectoRS/SCNet (#4604)

* Fix unittest

* Add COCO-Stuff docs

* Remove spaces

configs/detectors/README.md

@@ -15,6 +15,25 @@ We provide the config files for [DetectoRS: Detecting Objects with Recursive Fea
 }
 ```
 
+## Dataset
+
+DetectoRS requires COCO and [COCO-stuff](http://calvin.inf.ed.ac.uk/wp-content/uploads/data/cocostuffdataset/stuffthingmaps_trainval2017.zip) dataset for training. You need to download and extract it in the COCO dataset path.
+The directory should be like this.
+
+```none
+mmdetection
+├── mmdet
+├── tools
+├── configs
+├── data
+│   ├── coco
+│   │   ├── annotations
+│   │   ├── train2017
+│   │   ├── val2017
+│   │   ├── test2017
+|   |   ├── stuffthingmaps
+```
+
 ## Results and Models
 
 DetectoRS includes two major components:

configs/htc/README.md

@@ -17,7 +17,7 @@ We provide config files to reproduce the results in the CVPR 2019 paper for [Hyb
 
 ## Dataset
 
-HTC requires COCO and COCO-stuff dataset for training. You need to download and extract it in the COCO dataset path.
+HTC requires COCO and [COCO-stuff](http://calvin.inf.ed.ac.uk/wp-content/uploads/data/cocostuffdataset/stuffthingmaps_trainval2017.zip) dataset for training. You need to download and extract it in the COCO dataset path.
 The directory should be like this.
 
 ```none

configs/scnet/README.md

@@ -17,7 +17,7 @@ We provide the code for reproducing experiment results of [SCNet](https://arxiv.
 
 ## Dataset
 
-SCNet requires COCO and COCO-stuff dataset for training. You need to download and extract it in the COCO dataset path.
+SCNet requires COCO and [COCO-stuff](http://calvin.inf.ed.ac.uk/wp-content/uploads/data/cocostuffdataset/stuffthingmaps_trainval2017.zip) dataset for training. You need to download and extract it in the COCO dataset path.
 The directory should be like this.
 
 ```none

docs/1_exist_data_model.md

@@ -171,7 +171,19 @@ mmdetection
 │   ├── VOCdevkit
 │   │   ├── VOC2007
 │   │   ├── VOC2012
+```
+
+Some models require additional [COCO-stuff](http://calvin.inf.ed.ac.uk/wp-content/uploads/data/cocostuffdataset/stuffthingmaps_trainval2017.zip) datasets, such as HTC, DetectoRS and SCNet, you can download and unzip then move to the coco folder. The directory should be like this.
 
+```plain
+mmdetection
+├── data
+│   ├── coco
+│   │   ├── annotations
+│   │   ├── train2017
+│   │   ├── val2017
+│   │   ├── test2017
+│   │   ├── stuffthingmaps
 ```
 
 The [cityscapes](https://www.cityscapes-dataset.com/) annotations need to be converted into the coco format using `tools/dataset_converters/cityscapes.py`: