fix broken links in readme (#2098)

README.md

@@ -124,10 +124,12 @@ Within the following table, we summarized the current NNI capabilities, we are g
           <a href="docs/en_US/NAS/Overview.md">Neural Architecture Search</a>
           <ul>                        
             <ul>
-              <li><a href="docs/en_US/NAS/Overview.md#enas">ENAS</a></li>
-              <li><a href="docs/en_US/NAS/Overview.md#darts">DARTS</a></li>
-              <li><a href="docs/en_US/NAS/Overview.md#p-darts">P-DARTS</a></li>
-              <li><a href="docs/en_US/NAS/Overview.md#cdarts">CDARTS</a></li>
+              <li><a href="docs/en_US/NAS/ENAS.md">ENAS</a></li>
+              <li><a href="docs/en_US/NAS/DARTS.md">DARTS</a></li>
+              <li><a href="docs/en_US/NAS/PDARTS.md">P-DARTS</a></li>
+              <li><a href="docs/en_US/NAS/CDARTS.md">CDARTS</a></li>
+              <li><a href="docs/en_US/NAS/SPOS.md">SPOS</a></li>
+              <li><a href="docs/en_US/NAS/Proxylessnas.md">ProxylessNAS</a></li>
               <li><a href="docs/en_US/Tuner/BuiltinTuner.md#NetworkMorphism">Network Morphism</a> </li>
             </ul>    
           </ul>
@@ -224,7 +226,7 @@ Note:
 
 * If there is any privilege issue, add `--user` to install NNI in the user directory.
 * Currently NNI on Windows supports local, remote and pai mode. Anaconda or Miniconda is highly recommended to install NNI on Windows.
-* If there is any error like `Segmentation fault`, please refer to [FAQ](docs/en_US/Tutorial/FAQ.md). For FAQ on Windows, please refer to [NNI on Windows](docs/en_US/Tutorial/NniOnWindows.md).
+* If there is any error like `Segmentation fault`, please refer to [FAQ](docs/en_US/Tutorial/FAQ.md). For FAQ on Windows, please refer to [NNI on Windows](docs/en_US/Tutorial/InstallationWin.md#faq).
 
 ### **Verify installation**
 
@@ -288,7 +290,7 @@ You can use these commands to get more information about the experiment
 ## **Documentation**
 * To learn about what's NNI, read the [NNI Overview](https://nni.readthedocs.io/en/latest/Overview.html). 
 * To get yourself familiar with how to use NNI, read the [documentation](https://nni.readthedocs.io/en/latest/index.html). 
-* To get started and install NNI on your system, please refer to [Install NNI](docs/en_US/Tutorial/Installation.md).
+* To get started and install NNI on your system, please refer to [Install NNI](https://nni.readthedocs.io/en/latest/installation.html).
 
 ## **Contributing**
 This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit https://cla.microsoft.com.
@@ -304,7 +306,7 @@ After getting familiar with contribution agreements, you are ready to create you
 * If you have any questions on usage, review [FAQ](https://github.com/microsoft/nni/blob/master/docs/en_US/Tutorial/FAQ.md) first, if there are no relevant issues and answers to your question, try contact NNI dev team and users in [Gitter](https://gitter.im/Microsoft/nni?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge) or [File an issue](https://github.com/microsoft/nni/issues/new/choose) on GitHub.
 * [Customize your own Tuner](docs/en_US/Tuner/CustomizeTuner.md)
 * [Implement customized TrainingService](docs/en_US/TrainingService/HowToImplementTrainingService.md)
-* [Implement a new NAS trainer on NNI](https://github.com/microsoft/nni/blob/master/docs/en_US/NAS/NasInterface.md#implement-a-new-nas-trainer-on-nni)
+* [Implement a new NAS trainer on NNI](docs/en_US/NAS/Advanced.md)
 * [Customize your own Advisor](docs/en_US/Tuner/CustomizeAdvisor.md)
 
 ## **External Repositories and References**