Change theme for new homepage style (microsoft#641)

* Set theme jekyll-theme-cayman

* Set theme jekyll-theme-minimal

* Set theme jekyll-theme-slate

* Set theme jekyll-theme-cayman

* Update overview.svg

* Update README.md

* Update README.md

* Update README.md

* Update README.md

* Update README.md

* Update README.md

* Create overview.svg

* Delete overview.svg

* Update README.md

* Update README.md

* Update README.md

README.md

@@ -1,5 +1,5 @@
 <p align="center">
-<img src="./docs/img/nni_logo.png" alt="drawing" width="300"/>
+<img src="https://microsoft.github.io/nni/docs/img/nni_logo.png" width="300"/>
 </p>
 
 -----------
@@ -16,17 +16,17 @@ The tool dispatches and runs trial jobs generated by tuning algorithms to search
 
 ### **NNI [v0.5](https://github.com/Microsoft/nni/releases) has been released!**
 <p align="center">
-  <a href=#><img src="https://rawgit.com/QuanluZhang/nni/update-doc11/overview.svg" /></a>
+  <a href="#nni-v05-has-been-released"><img src="https://microsoft.github.io/nni/docs/img/overview.svg" /></a>
 </p>
 <table>
   <tbody>
-    <tr align="center">
+    <tr align="center" valign="bottom">
       <td>
-        <b>User Code + SDK( import nni )</b>
+        <b>User Code</b>
         <img src="https://user-images.githubusercontent.com/44491713/51381727-e3d0f780-1b4f-11e9-96ab-d26b9198ba65.png"/>
       </td>
       <td>
-        <b>Tunning Algorithm Extensions</b>
+        <b>Tuning Algorithms</b>
         <img src="https://user-images.githubusercontent.com/44491713/51381727-e3d0f780-1b4f-11e9-96ab-d26b9198ba65.png"/>
       </td>
       <td>

_config.yml

@@ -1 +1 @@
-theme: jekyll-theme-dinky
+theme: jekyll-theme-cayman