update doc about nni docker image (#345)

deployment/docker/README.md

 Dockerfile
 ===
-## 1.Description  
+## 1.Description
 This is the Dockerfile of nni project, including the most kinds of deeplearning frameworks and nni source code.  You can run your nni experiment in this docker container directly.
 Dockerfile could build the customized docker image, users could build their customized docker image using this file.
-## 2.Including Libraries  
+This docker file includes the following libraries on `Ubuntu 16.04 LTS`:
 
 ```
-Ubuntu 16.04 LTS
 CUDA 9.0, CuDNN 7.0
 numpy 1.14.3,scipy 1.1.0
 TensorFlow 1.5.0
 Keras 2.1.6
-NNI v0.1
+NNI v0.3
 ```
 
-## 3 How to run  
-    
+## 2.How to build and run
+__Use the following command to build docker image__
+```
     docker build -t nni/nni .
-    nvidia-docker run -it nni/nni
+```
\ No newline at end of file
+__Run the docker image__
+* If does not use GPU in docker container, simply run the following command
+```
+    docker run -it nni/nni
+```
+* If use GPU in docker container, make sure you have installed [NVIDIA Container Runtime](https://github.com/NVIDIA/nvidia-docker), then run the following command
+```
+    nvidia-docker run -it nni/nni
+```
+or
+```
+    docker run --runtime=nvidia -it nni/nni
+```
\ No newline at end of file

docs/InstallNNI_Ubuntu.md

@@ -20,6 +20,10 @@
       cd nni
       source install.sh
 
+* __Install NNI in docker image__
+
+    You can also install NNI in a docker image. Please follow the instructions [here](../deployment/docker/README.md) to build NNI docker image.
+
 ## Further reading
 * [Overview](Overview.md)
 * [Use command line tool nnictl](NNICTLDOC.md)