add webui screenshot in README.md (#323)

* update doc

* update

* update

* update

* add logo

* logo

* logo

* update

* update installation doc

README.md

-# Neural Network Intelligence
+<p align="center">
+<img src="./docs/img/nni_logo.png" alt="drawing" width="300"/>
+</p>
+
+-----------
 
 [![MIT licensed](https://img.shields.io/badge/license-MIT-yellow.svg)](https://github.com/Microsoft/nni/blob/master/LICENSE)
 [![Build Status](https://msrasrg.visualstudio.com/NNIOpenSource/_apis/build/status/Microsoft.nni)](https://msrasrg.visualstudio.com/NNIOpenSource/_build/latest?definitionId=6)
@@ -27,6 +31,7 @@ The tool dispatches and runs trial jobs generated by tuning algorithms to search
 ```bash	
     python3 -m pip install --user --upgrade nni
 ```
+Note: If you are in docker container (as root), please remove `--user` from the installation command.
 
 **Install through source code**
 * We only support Linux (Ubuntu 16.04 or higher) in our current stage. 
@@ -74,6 +79,13 @@ You can use these commands to get more information about the experiment
 -----------------------------------------------------------------------
 ```
 
+* Open the `Web UI url` in your browser, you can view detail information of the experiment and all the submitted trial jobs as shown below. [Here](docs/WebUI.md) are more Web UI pages.
+
+<table style="border: none">
+    <th><img src="./docs/img/webui_overview_page.png" alt="drawing" width="395"/></th>
+    <th><img src="./docs/img/webui_trialdetail_page.png" alt="drawing" width="410"/></th>
+</table>
+
 ## **Documentation**
 * [Overview](docs/Overview.md)
 * [Get started](docs/GetStarted.md)