Update install scripts (#3290)

* Update install scripts

* Update installation of mmcv

docs/install.md

@@ -45,8 +45,14 @@ conda install pytorch=1.3.1 cudatoolkit=9.2 torchvision=0.4.2 -c pytorch
 If you build PyTorch from source instead of installing the prebuilt pacakge,
 you can use more CUDA versions such as 9.0.
 
-c. Install mmcv, you can [install](https://github.com/open-mmlab/mmcv#install-with-pip) the pre-build mmcv.
-Or you can choose either to compile mmcv from source by the following command
+c. Install mmcv, we recommend you to install the pre-build mmcv as below.
+
+```shell
+pip install mmcv-full==latest+torch1.5.0+cu101 -f https://openmmlab.oss-accelerate.aliyuncs.com/mmcv/dist/index.html
+```
+
+See [here]((https://github.com/open-mmlab/mmcv#install-with-pip)) for different versions of MMCV compatible to different PyTorch and CUDA versions.
+Optionally you can choose to compile mmcv from source by the following command
 
 ```
 git clone https://github.com/open-mmlab/mmcv.git
@@ -138,6 +144,11 @@ conda activate open-mmlab
 
 # install latest pytorch prebuilt with the default prebuilt CUDA version (usually the latest)
 conda install -c pytorch pytorch torchvision -y
+
+# install the latest mmcv
+pip install mmcv-full
+
+# install mmdetection
 git clone https://github.com/open-mmlab/mmdetection.git
 cd mmdetection
 pip install -r requirements/build.txt